Having no 2 or 3 factors should be worse than a single 2 or 3. Having no 2 factors leaves roughly half the numbers as candidates. Being divisible by 2, but not 4, limits it to about a quarter.
I've never seen the code for how xdle works and how it chooses its clues. A strict priority list of what clues it prefers follows what I've seen. I do know it's deterministic and not random as the same puzzle returns the same clues if the input is the same. I am not aware of it not giving a "perfect square/cube/4th power...etc." clue when that's an option.
As for the 10/8 puzzle, I decided 20 * 13 was good enough, and got it in two clues. That was pure luck. I would have done the same if I started at 512. In that case, it switches to "x<252; (252-x) is prime," narrowing it down to just 239.
Getting the "(252-x) is prime" clue is what I'd expect, based on what I think the clue priority list is. Similarly, if I guess 303 today, it gives "(303-x) is a 6th power."
Understanding that there is this hierarchy of clues can help eliminate some clues. When I bother to look deeper as I have above, projecting what sequence of clues it would give one or two steps down the line can reduce the number of guesses.
Finally, I'll note that, unlike Dordle, for xdle, I only guess numbers that are possible solutions. I wouldn't do your (512, 243) scheme unless it fit. I don't make impossible guesses frequently in Dordle, but sometimes they're necessary to eliminate several letters at once.