Well, in a discussion about balancing encounters, creating "fair" fights, and the role of players and GM in meeting expectations around those subjects, it makes sense to investigate what, exactly, is demanded of the players.
My experience with GURPS overwhelmingly points to the fact that players are expected to spend non-trivial amounts of time away from the game table learning how to "optimize" and "maximize" their individual character potential. Literally every player (other than me) in my GURPS groups would spend hours each week looking through the various magic/psionics/shamanism books. They'd go through the martial arts handbooks. They'd pore through the tech and gear manuals.
Why? I expect it's because they were hoping to "unbalance" and "un-fair" the fights in their direction.
This is an important part of the conversation. If the expectation is that players should spend little to zero time away from the table, then it's on the GM to work to "balance" and "create fairness" for encounters.