[edit: Rereading your comment, I think we are talking cross-purposes. I'm talking about heads up games only. You said "Heads up, where there is an optimal strategy, is essentially solved," I replied that "this is wrong, although there is a solution, it's far from solved..." and the conversation went from there. It seems at some point you switched to talking about ring games? On that I obviously agree, Nash does not apply.

So I maintain everything i said before; HU games are far from solved. Much the same that chess is far from solved.]

The game of poker is symmetrical and zero-sum (ignoring rake).

As you say, "Nash is a strategy where no individual has a motivation to change from the equilibrium." If I were playing a GT optimal strategy, the best you can do yourself is play the same strategy - you are not motivated to deviate. This will be EV neutral to both of us in a symmetric, zero-sum game.

Any deviation you make will either be EV neutral and therefore indifferent, or EV negative. If it is EV negative to you, I gain.

Of course none of this applies to multiway games, we're talking heads up.