Seems a little odd since he has an average of 30ish in tests
He has an average of 50 in FC cricket which probably shows he has trouble adjusting to unfamiliar conditions

There's more to it than his f/c or Test average. Some of the best coaches (or technical advisers) never played professionally in the sport they coach.

Obviously, plenty played and were right at the top. But it's not a given that the best coach will have done that. Moreover, often the better technical coaches weren't the most gifted if/when they played the game. They are often excellent at advising on technique because they weren't blessed with every natural athletic gift. Whereas the supremely gifted may not have to deal with technical problems and thus might not be that great at helping young cricketers with such things. So they (the less talented) had to think long and hard about the technical and tactical side of things to succeed. E.g. Chris Rogers as a batsman. Technically very solid but not as innately gifted as some of the other better batsmen. Still gifted but not quite as naturally talented as others. Yet, he was far more successful than many batsmen who probably possessed more natural talent. The kind of advice he could bring would  be invaluable to young batsmen.

Then the likes of Ricky Ponting is naturally one of the most gifted and also knows his game inside out.

But don't assume great or talented cricketer means great coach. While less talented or successful cricketer means inferior coach. It doesn't always work that way.

As for Graeme Hick specifically... it wasn't necessarily a case of him having trouble adjusting to unfamiliar conditions (although that may have played a part).

The main problems for Hick were, apparently, technical and mental. I've heard tell he mightn't have been as mentally tough as others who did better. But he was also rather weak against the short ball, apparently. He flourished in England in county cricket where the quality of bowling (with respect to short-pitched deliveries) was not high enough to find out his weakness. Then in Test cricket, good bowlers punished this.

It's a bit like those Australian batsmen who are flat-track bullies and then look like schoolboys when there's a hint of lateral movement. Both are technical fundamental technical weaknesses.

That wouldn't seem to be encouraging for Hick as coach. But maybe he's able to help others address their technical issues better than he did his own.

most aussies have their first class average converge with their test averages

his was 20 runs below his first class average despite a long career

If it was a technique problem with the short ball there are plenty of places where it doesn't bounce much
Perhaps he was mentally soft as well as you mention
but thats not a great thing to have in a coach!
Nervous coach means nervous players!

Graeme Hick was an immense talent who was from Zimbabwe before they had a test team. He had to play years of county cricket while waiting to qualify to play test cricket which turned him into a bit of a flat track bully. He dominated county cricket with ease and that hurt his game greatly. It also meant he entered test cricket with massive expectation that he would be a star which he never realised.

Yeah but grazorblade, world-class bowlers can do damage on most wickets against batsmen who have a fundamental technical weakness against short-pitched deliveries.

His f/c average was so much higher than his Test average because, despite doing brilliantly in County cricket, his weaknesses got exposed when he played at a higher level.

It's a bit like Adam Taggart's scoring record in the A-League compared to in higher quality competitions.

And there would be Aussie batsmen who have excellent Shield records but have done poorly in Test cricket. Possibly such batsmen have their Test stats helped by virtue of the fact that Australia plays a heck of a lot cricket at home on roads against weak opponents. But such batsmen, when they go to the Subcontinent or England, and the ball is suddenly spinning, seaming and swinging, they become walking wickets. I gather Hick was a bit like this with the short-pitched delivery.

You seem to be very good with statistical analysis, grazorblade, so look at it this way...

Only pseudo-statistical, but anyway. The County Championship in the 80s and 90s did not have plenty of world class bowlers. England only had a few really good pace bowlers, such as Darren Gough and Ian Botham. Both were very good. Neither was a true great though, as bowlers go. There was the odd West Indian, Pakistani, South African, Kiwi and Australian playing in the County Championship who was world-class. But there would have been a lot of mediocre bowlers. And in the context of that dilution in quality, those bowlers wouldn't have been that skilled at short-pitched bowling.

So basically, Graeme Hick encountering attacks with, at most, one very good to world class fast bowler. He would have been facing a lot of average bowling. And he did brilliantly against such bowling. More to the point, that type of bowling didn't test (or allow him to improve) his fundamental technical weakness.

Then, suddenly, Graeme Hick finds himself playing Test cricket. The amazing think about Test cricket is that each country can, usually, gets its best cricketers playing it. So Hick goes from facing lacklustre attacks with, at most, one very good bowler to facing attacks with sometimes four world class fast bowlers. There are not so many freebies and nowhere to hide. Plus, the 90s was a golden era in terms of the quality of fast bowling. Think about Hick facing attacks containing, in any given match, all or many of:

West Indies- Malcolm Marshall, Courtney Walsh, Curtley Ambrose, Ian Bishop

Pakistan- Wasim Akram, Waqar Younis

Australia- Craig McDermott, Damien Fleming, Glenn McGrath. Plus, Shane Warne (who is a leg-spinner, not a fast-bowler, but of a quality rarely seen in the County Championship)

South Africa- Allan Donald, Shaun Pollock, Makhaya Ntini, Jacques Kallis, Craig Matthews

Hick did have a quite successful middle section to his career, he averaged over 45 in a three year period. Not nearly enough to say he utilised his talent fully. If we look at a number of Australian players such as Hayden, Langer, Martyn, Blewett and I am sure others, they had a short period in the test team when young and then spent time away improving their game so that they came back better and (apart from Blewett who still was not that successful) had much better careers. Hick never had that opportunity because of his fairly unique circumstances. 

Hick was immensely talented, but had no problems with short pitch bowling or the like imo. Hick spent 7 years in County Cricket where nearly every team had a West Indian enforcer bowler before he played test cricket. The whole world waited for his eligibility cos he scored a 400 odd very young and early on in the piece.

He made massive test runs against the 1995 West Indian attack of Ambrose, Walsh, Bishop and Benjamin. He did not have technical flaws for them to expose.  He was elegance and grace. He made plenty of runs in India against Kumble and co. He made runs in Safrica against Donald, Schultz and Pollock. The first two being lightning fast bowlers, the first one a lefty at that. But Akram felt that he did have Hick's measure with short balls. But then it could have just been picking up Akram's action which more than a few batsmen struggled with over the years, tbf.

Hick did however suffer to sledging. The "fat track bully" comment was itself a sledge by famous NZC sledger John Bracewell. And it followed him around. Merv Hughes was famous for sledging him into making mistakes. 

Once the secret was out, everyone had a go at it and he had a long awful dismal end to his career from 1996 to 2001 which just wrecked his test average. The sledging didn't impact on his ODI game as much, and he made huge runs in Aus in 1998/99 where he scored 3 centuries, 1 unbeaten, and a not out 60 odd in 4 consecutive innings.

So noone really ever questioned his talent or abilities. Like Ramprakash, he just failed to execute. Now the theories and unluckiness of Ramprakash are endless. Try explaining these numbers...

http://www.espncricinfo.com/england/content/player/19323.html

Vinod Kambli, Tendulkar's school kid partnership batsman, he is the one who famously was dropped with a test batting average over 54. He HAD A PROBLEM with the short ball that was found out in tests. The West Indies and NZ destroyed him after he started his career like Bradman against Eng, SL and Zimbo. 

http://www.espncricinfo.com/england/content/player/19323.html

I wondered what happened to Kambli?