Originally Posted by SamSam77

Thanks for your suggestions.

Regarding the B-screw adjustment, what I meant was that I have loosened the screw (bringing the chain closer to the cassette) to a point where the screw is no longer pushing on anything and further loosening past this limit has no effect.

Yes, the cassette is the same model/type. My gearing is 3×9.

Although the old housing was reused, and thus suspect in the context of this problem, as near as I can tell it is undamaged and the cable slides effortlessly through it. The length of the housing was unchanged following the derailleur replacement. With the new derailleur, there is now noticeably less slack in the housing routing compared with using the old derailleur (i.e., there used to be a much larger 'loop' of cable/housing at the rear derailleur that is now mostly taken up).

I did check/realign the derailleur hanger (with the tool) in the course of the replacement and afterward (by eye) the derailleur appears to hang pretty straight.

A composite photo of the installed derailleur, for reference, can be seen here.