Today I moved the derailleur cable to the other (proper) side of the fixing bolt and readjusted the tension. The issue is definitely not completely fixed but I think it might be slightly improved. The lag in shifting is most noticeable at the extrema of the cassette (i.e., cogs “1/2” and “8/9” in my case), but I think in the middle it might be better. If the cable being on the wrong side of the bolt was at least partly to blame for the issue, then I am very surprised and happy to be wrong about it. More testing to come in the coming week’s commute.