Hello! I want to confirm that I understand what GTO is, that my view on GTO seem sound and I also want to ask a question about it!

So I strictly bumhunt headsup-cash. That means that I should definitely play exploitatively as fish has obvious leaks. To be able to exploit as much as possible I need a very sound game-theory knowledge base. I dont want to (nor can I obviously) play GTO vs fish that i have located leaks on.

What I think GTO is:

GTO is an unbeatable strategy with perfectly balanced ranges in all spots, completely unexploitable. Say that two GTO-bots or humans with the potential to play GTO starts playing each other. They might play different at first. They start to adjust to each other. They readjust to their opponents adjustments. They readjust to their opponents readjustments. They continue like this for X amount of time untill they eventually reach an equilibrium point. At this point none of the players will want to adjust anymore as it would be -ev.

I cant wrap my head around this! How can GTO can be "unbeatable"? Say that one of the players defend the majority of their bluffcatchers in a river spot. Wouldnt it be best then, for the other player to lower their bluffing frequency from the GTO amount to a lower one? As an exploit in that specific river situation? How can a strategy be unbeatable? Isnt there always a counter strategy to any given strategy???