If you're playing in the smaller stakes games, micro games, or if you're playing against bad opponents constantly &you don't need GTO. If you're playing against good players often, if you're playing heads up a lot of the time against good players & GTO is going to be way way way more important.

Can I learn to beat GTO players? Technically, no. If someone is playing perfect GTO strategy, then the best you can do is to play the same perfect GTO strategy back at them and break even. Even then, in most games, you'll lose since there's rake in cash games and a house fee in tournaments.