from what i hear bitwig isn't very optimised in the first place anyways, so who knows. maybe audiotool really is just unoptimised and bitwig is just REALLY unoptimised? :-D but i hear this from years ago. maybe they fixed it by now. its also been a while since i've used ableton and FL, can't be hard to experiment yourself with the trial versions if you are genuinely curious how audiotool compares. just trying to share my personal anecdotes
audiotool runs better than other daws such as FL, ableton and bitwig, that is all i can say. on par with minimalist daws like reaper. tracker-style daws would probably be even more "optimised" but at that point you are relying on whatever VSTs you are using to be optimised
i normally just zoom into an empty part of the draft if i want to hear the timeline without lag