Qualified immunity would protect prosecutors from frivolous suits, IF THEY FOLLOW THE ACCEPTED RULES.
The problem here is ABSOLUTE immunity - i.e. there ARE no rules for them. Prosecutors, like the rest of us humans, don’t sport wings and halos - they’re not immune to selfishness, hatred and other base emotions, regardless of their title and professing how ethical they are.
NO ONE should be unaccountable.
That said, anyone bringing a case against a prosecutor should have to prove that the prosecutor was guilty of some minimum standard of abuse of authority, or their lawyer gets disbarred and they have to pay for the prosecutor’s legal defense - and maybe they should have to post a bond to secure that payment. Such an arrangement will weed out 95% of frivolous suits.
But the idea that prosecutors should be utterly immune for ANY act, no matter how heinous, that they commit while wearing their prosecutor’s hat is absurd and unjust in the extreme.
You obviously have no experience in the legal system so your idealistic notions are great for a classroom but utterly fail in real life.