It’s more than just lack of hairs.
There are changes in the scalp skin by the time severe MPB has really wiped out all the hair growth. It’s shinier, tighter, oilier, and I think it’s actually a bit thinner.
As far as I know, this skin changing process has not proved permanent and irreversible though. Stick a bunch of transplanted follicles into the area, and it eventually reverts to its original pre-MPB situation to nourish them. I haven’t read anything about ultimate transplant limitations in these areas being lower than in healthier skin.
Although I remember reading at least one of the major HT clinics had a policy of not fully dense-packing an area like this in a single first HT session. They’d do a first pass with only partial or 2/3rds of the final density they wanted in the area, and then finish the packing on a later HT pass at least 9 months or year later. They said this seemed to help improve the graft survival.