I think that one solution is to make being a prosecutor a political dead end. In other words, convince the public to never, under any circumstances, vote for anybody who has ever been a prosecutor (except perhaps if the position in question is prosecutor, though excluding this exception would be creating de facto term limits which might be a good idea anyway...).

That way somebody only becomes a prosecutor if being a prosecutor is what they actually want to do with their career in public service. It would not be a stepping stone for a further career in politics.

If term limits (de facto or de jure) existed for prosecutors, that would put the brakes on prosecutors optimizing for conviction rate.