I liked your post Donny... It could almost be said as a metaphor for things in life as well... You can be doing something one way your whole life and get better faster at it, and are quite content,,, then someone comes along and shows you a better way, and you almost have to look back on every single time that you did that thing, and wondered why and how you ever really truely got by without that new piece of knowledge...

As Missy said, I think it is all your hard work and determination that got you to the level that you made it to, and it is that exact some drive that will take you to the level above that if you wish..

One way I would suggest to look at it is by watching a few boxing matches... Many many many fighters have different stances and techniques. They all hold their hands differently, move differently, stand a little different, throw their punches slightly wider or shorter etc... Any one of them could have been throwing like that their whole boxing career, and they could be 5 time world champions....... To a new person coming in, they would probably even try to emulate exactly how that champion throws their punches/stands..... But a different trainer could come along and show that champion a different way of throwing a jab, and instantly it could improve.....
It probably doesn't make his last trainer's jab inferior. Hell it got him 5 world championships..
Everyone has different styles and techniques.. And what really works for one person.. In fact, what is absolutely perfect for one person might be quite inferior for another...
That new trainer showed you a few tips that fortunately are something that suits you and where you can progress from where you are now, and it seems like your old techniques weren't as good as the new ones...
That's very lucky for you, and you sound very grateful for the gift... But I wouldn't think of your last trainers instruction as inferior to the new trainers... Just different, and not 100% perfect for you yourself...

I remember watching a documentary with Wayne Mcculloch when he changed trainers, and the new trainer said to him, "show me your jab"... Wayne does a Jab.. trainer says "Is that how you always throw it?", Wayne says "I'll throw it however you want me to throw it"...

Wayne was already a chapion at this stage, and his new trainer was able to improve his Jab... But it's the heart and determination that makes a champ...

My final thought is,,,, there are fighters who have made very decent professional careers, and have 100% taught themselves!!! Anyone could question just how far they could have got if they had proper instruction... But maybe they might not have got anywhere?? Millions of other factors could have determined them not being champion if they had adopted a trainer instead...

So take the new gift and enjoy it and let it make you all the more better of a fighter... And remember that it's everything that can't be taught that has probably got you as far as you are now, and further...