>But if you don't explore a line, even if you believe it's effectively useless, then you haven't solved chess.

That's actually a good point because ideas that modern GMs found to be useless (in particular, locking a wing down via aggressive early wing play) have actually found a new home in AlphaZero's play.

What might be completely dumb from an early move (say, aggressively pushing the F pawn from the start) might provide to be an incredible opening, but humans are too stupid to be able to execute it perfectly.