Alternatively, we understand it well, and discard bad completions immediately.

When I'm using llama.vim, like 40% of what it writes in a 4-5 line completion is exactly what I'd write. 20-30% is stuff that I wouldn't judge coming from someone else, so I usually accept it. And 30-40% is garbage... but I just write a comment or a couple of lines, instead, and then reroll the dice.

It's like working through a junior engineer, except the junior engineer types a new solution instantly. I can get down to alternating between mashing tab and writing tricky lines.