To the extent you know what the GTO play is, sure make that your default approach. In a lot of spots though, it's tough to say what's GTO. For example, if I'm playing a GTO strategy with 30bb on the button in a full ring game, am I supposed to open-limp at all?
Where you do know what the GTO line is, you can also do better if you can make correct exploitive adjustments (particularly against weak players who make significant mistakes). As an example, if you bluff the river with GTO frequency versus a maniac who never folds, you'll still get the better of him. But you can improve your results in this extreme case by only value betting and never bluffing.
I agree completely. I think, the most important concept is, that against most opponents we need to be reasonably well balanced in all situations. We cant for instance have one raise size preflop, we only use with aces or kings, another one for our baby pairs, and then a third one for the rest of our range. It need to always be, so that our opponent cant put us on just one single type of hands.
And likewise when we are facing aggression, we need to avoid having spots, where we always call, or where we always fold, especially against players who are really good or really bad, because we have less chance of knowing, what they are doing.
So instead we need to call with the top of our range, so that we are calling enough of the time. In GTO language follow our "minimum defense frequenzy". In traditional live poker language "He is representing a monster, but my hand is just to good to fold" - "nice hand sir" (muck his cards).