on the gwa choi ( back fist ) yes i have and actually against a boxer in a ring fight, guy was golden gloves and all in all it was an interesting experiance from both sides, basically it scared the cr@p out of him, because it isn’t something he was use too or had encountered in the ring. he wished to stay away from kicks and i wished to stay away from being limitted in my use of hands, so it was a compramise. the fight however was a public fight but on the quiet side of things hahaha.
the question you ask must come from personal experiance i suppose, from mine, i find if you walk into the ring with rules governed by a particular fighting skill, then more than likely you will find the rule governed skill will come out on top.
now i have heard things like it shouldn’t matter what the rules are you should be able to win no matter what, but this is childish and small minded thinking, to walk into a skilled players rules you should expect an extremely hard time no matter what and if anything a great disadvatage, this is why muay tai fighters do so well, in their art, none can beat them with their rules, well except in the 1950’s ( thailand ), oh ok then also the 1970’s ( thailand ) but no others 
you have to also look at what is being seen, for every good fight you see on tape or on t.v. etc, there are thousands of boxers, muaytai, or whatever not as good, with gung fu or cma in general the level of skill seen is not really shown.
in asia especailly in the 50’s - 70’s and maybe into the 80’s there where some extremely good fighting , but these days it has been watered down due to rules, gloves, body protection, timed rounds etc, different time i suppose know.
i take nothing away from any of the skills you have mentioned, a good fight is a good fight and a skilled player is great to watch.
as to why they develop faster, i am not sure what measure you are using i have seen many martial arts have good young fighters with great raw skill, so i don’t see any disadvantage on that part, maybe it all comes down to who teaches them, these days anyone can open up a school, say this and that, next thing you know out comes the rubbish.
in older days if they teacher wasn’t good, then he would be closed down, sometimes the old ways are better lol