Of course it would be better for almost everyone if Trump stepped down from the race rather than Biden.
We can ask Trump whatever we want. Since he has a dictatorial grip on the Republican Party, it will be ineffectual.
On the other hand, Biden is a good guy, who will presumably bow to the will of the Party and heed a good argument, if, and that is still a big IF, there is a charismatic candidate with a significantly better chance. The election isn't today or tomorrow so that may happen.
But "asking" Trump to leave the Race? That will have zero effect and we will just be deluding ourselves.