im no gm of course but my repetoire personally is based on what sort of positions agree with my intuition. I like solid stable positions where nevertheless pieces have decent scope and there is possibility for some tactical imagination. If a person cant visualize as well as i could when i started playing i would be at a loss on how to help them :P Also if a person is very strong in ultra chaotic positions i would simply consider it mystical. I have no idea how people navigate a complete mess. If a person knows how to win from a position that looks totally blocked to me, then again my approach to positions would be leading them away from their strengths. I know that stronger players are naturally going to be mroe flexible but they still have limits and you want the most bang for your buck.
What you say makes perfect sense.
But... there is another side of things.
2 of the very best players were Kasparov and Alekhine. Both were natural tacticians and attacking players. Both had to defeat the previous world champion to achieve the titale themselves, and both had to master simpler types of positions to do so. This has a lot to do with why they became so strong.
This isn't just my opinion, why listen to a much lower rated player, but Kasparov says [well implies] this about himself in his books on the rivalry with Kasparov, and quotes Karpov's statements saying something similar.
To talk about me for a bit, when I was much younger and trying to improve, one of the best things I did was I decided I had trouble evaluating positions with material imbalance. As a remedy I decided to play gambits in lots of casual games. My one time weakness is gone and I may be better at that than most players my strength.
Coming to your comments, if my reasoning is sound, you should consider playing wild and blocked positions, casually not in important games at first, and studying that kind of position. Navigating a complete mess is not something mystical, it can be improved by practice and study. Ditto blocked positions.
It is at least something to consider.
When selecting a chess coach, how important is it that the coach play similar openings to what I currently play. For example, should I exclude a coach because I am a 1. d4 player and the coach in question plays 1. e4. Or I play 1. ...e5 as black but the coach is a lifelong 1. ...e6 player.
How much should I let title (GM,IM, etc.) influence my decision? If I'm a 1900 USCF for example, is selecting a NM coach going to give me the improvement I'm after?
GM's know a lot about every opening and could give you a good repertoire whatever you play. For instance, pfren could tell you a lot about either the Benoni or the English, which are both quite different.
I ain't a GM, and I don't know the Benoni sufficiently well (unlike the Benko, which I have used many times as Black, and which is very different than the Benoni). In all probability, my wife is more proficient to it than me. I can teach the Benoni to anyone (anyone?), but I must do some homework first- as well as any decent trainer regarding the XYZ opening.
What do you think of this set up against the Benko?
Not sure if I remember it well though.
4...g6 is not bad, but rather stereotypal.
4...bxc4 is a better move, when after 5.e4 Black can play safely and consistently (5...e6) or more enterprisingly (5...c3, 5...g6).