I'll try to answer since I have over @130 stays on property and @35 of those at POP Century AND I have stayed at B Resort in most their room options about 5 times.
OP says they understand the on/off reasoning. I get onsite only folks don't get the offsite benefits and visa-versa but there are huge perks both ways that can't be replicated by the other. OP says they have their own preferences and maybe they fall in to some I can think of ...
Including what
@writerguyfl says .... B Resort is much nicer than POP Century .... especially for an adult or solo adult.
B Resort ...
... rooms are much larger with ample space to move around, some with sofas and balconies or views
... rooms are decorated modern, boutique and less sterile than the new POP rooms
... some rooms facing pool have balconies to enjoy or nicely furnished private patios that have pool access
... rooms are interior hallway entry, potentially much safer for a solo traveler
... bathrooms are large and modern and well done
... pool is usually quiet with very nice pool bar right there, nice loungers with pool towels right there
... pool deck area has outdoor lounges and nice furniture if you just want to relax
... grab and go is one of best I have seen and right by pool
... Table Service dining that has only had good reviews I have seen
... Nice indoor bar
... Good bus shuttle to parks
... Walking distance to Disney Springs, which as adults is a nice perk for dining and evenings
... This year, 60 day FP+ and EMH
If comparing one to the other the only plus POP brings is Magical Express. But then again, many folks don't like that system and still pay for taxi/etc to get them to hotel especially returning to airport.
The reason one would pick offsite for the same price is because they will almost always get much more for that same price. Right now I have 4 nights booked at POP in the fall with a discount. For the same exact price I can book B Resort in a two room executive suite in the tower. We are talking apples and oranges here. I'm tempted to book this but ...
For about $100 less I can book a FULL WEEK in a 1 bedroom condo with kitchen, porch, much nicer pools and amenities. Since I have a car and AP ... I can drive to parks faster than I can ride a bus, I park for free .... so for a week = $920* for POP OR $420 for a nice condo resort almost no brainer. But seriously, how is POP worth a thousand dollars for a week? and that is with a good discount!
* POP rate is probably more since I just took my weekday rate x 7 and we would have to add two weekend rates to that probably hitting $1000.