This is exactly wrong. At the highest levels you play your opponent, not only GTO. No one can play pure GTO and you exploit how your opponent moves off GTO.
The players who study GTO instead of trying to win these meta mind games have proven to do very well in online heads up while the old-school mind games guys keep going boom and bust.
An online $100/$50 heads up match is probably equivalent to a $10k/$5k live game, in terms of the quality of pros you'll find grinding them.
What do you think represents the highest level of poker instead?