Sorry, Yohan, to be a pain in the ass, but your post just proves my point even further.:)
GTO is a 100% static strategy, that makes you at least 0EV versus every possible counterstrategy. You cannot throw in stats or assumed ranges, cause GTO does not care about the opponent's strategy or range or whatever. GTO is an absolute static strategy, that will never lose against your opponent. The definition of GTO is not up to me, it's a really basic game theory definition that I'm not gonna go into. But anyway, the point is GTO is the same whether you play against a loose-passive fish or a maniac.
I reality, the GTO play will, as far as I can see, very rarely deviate substantially from basic EV calculations.
This is where you're awfully wrong. Any purely exploitative strategy will deviate from GTO or balanced plays a lot. Imagine a very simple 1 bet 1 street AKQ game. The GTO here is bet all your As, and alpha amount of Qs. The opponent's GTO-reply is to call with Ks a given amount of the time. However, if the opponent just bets a tiny bit more Qs, your maxEV (=/= optimal) response is to call with all of your Ks, and if the opponent bets a tiny bit less Qs, your maxEV response is to fold all Ks. Therefore that really really really small percentage in his strategy matters 100% in our strategy. So you can see how substantially GTO (that always call x% of Ks) differs from basic EV calculations.
What you cannot really throw in is making assumptions about adaptions on part of your opponents. That would really be stretching the terminology past a point of appropriateness. Then it would enter a territory where no GTO has been proved to exist (as far as I know) mathematically.
Once again, I don't get that part, or if I assume I get it, than you're wrong again. GTO is a strategy you can use in any circumstance coming up. There is no right adaptation against it, and since adaptation in itself is not a strategy, but a change in a strategy, there can be no GTO for that.
An interesting truism about GTO: It is optimal if and only if the opponent plays GTO himself. Corollary: GTO is never optimal, since nobody can play GTO.
Sadly, it's not a truism. It's maxEV only, if your opponent plays GTO himself. MaxEV is not optimal. Optimal means, that there's no succesfull counterstrategy against it. Also, it provides us with the great feature that against a completely unknown strategy, it's EV is >= than the EV of choosing another random strategy. (Not the EV of a random strategy, you might accidentally choose a better EV line, but if you choose randomly, the average EV will never be higher.)
If you wanna hear a more successful player's opinion on it, listen to one of the latest 2p2 podcast with sauce, he says awesome stuff in this matter.
But all in all, no one said you should play GTO, however the more I learn about poker the more I believe in that it is a necessity to know as much as possible about GTO, because that can help you shape your strategy in ways a pure exploitative player will never be able to. I see plenty enough evidence proving it at the tables, but if you look around the forums or videos you can get a feel for it too.