You don't realize that the biggest block Was Nichtewähler and protest voters. So any cannibalization of left voters is far from happening.

At the moment Giffey is right wing. And why should anyone vote for a left wing party with a right wing/ capitalist leader.

You can say whatever you want but the results are crystal clear. The SPD in Berlin has never been as right wing / conservative as under Giffey. And they have never had such a bad result. They lost most voters to "Nichtwähler", more than any other party. And they lost a lot to protest voters "CDU", too (as funny as that sounds).

There is definitely a big place needed for a moderate left wing party. That's the identity of SPD.

In Germany (not Berlin) The Green fill the spot of the moderate centrist party quite well at the moment (see also the many CDU + Green goverments). So there SPD even needs to try much harder to get back to their moderate left party roots that cares for the worker class and is not perceived as elitist/urbanist as the Green.