Qualified immunity concerns civil liability. Prosecution is about criminal liability.

Civil liability is helpful because tax payers do care about $$$ (if judgements/settlements are starting to eat major part of budget the people will start to care on how to lower those costs) and victims are not limited by what prosecutors are ready to do. The QI is especially problematic because it has essentially become "did someone prosecute cops about this before" because that's effectively the only way to establish precedence that allows you to get across the QI-line in future for sufficiently similar conduct. And like you said, prosecutors are often unwilling to prosecute cops.

Civilly you can still overcome QI without prosecution, but it's indeed a lot harder to do.

Regardless, IMO, criminal prosecution is the thing that's truly lacking. It's not as if there aren't criminal codes around government officials violating constitutional rights, there are [1]. It's just that they go mostly unenforced.

This cop should be in jail on 700 counts of violating the 4th amendment.

[1] https://www.justice.gov/crt/deprivation-rights-under-color-l...

Yes and the burden of proof standard is typically lower in a civil case than it is in a criminal proceeding. So a prosecutor may very legitimately not bring a criminal case if they feel they can't meet the "beyond a reasonable doubt" standard, but the same evidence brought in civil court could very well win the day. So the civil suit path could still be a deterrent to bad behavior if not so severely throttled.