Before my mom had cancer and subsequent surgery for it, she was also well above that 250lb limit. She has had asthma and COPD for years and years and refused to use a scooter or wheelchair. So I understand the pride thing. She missed out on so much on so many WDW trips for so many years. The rest of the family went on ahead to ride multiple rides while she waited on a bench. She couldn't keep up, and she couldn't breathe. After years of nagging, on one trip back in 2008, I finally FINALLY got her to agree to try a rented WDW scooter at Epcot for one day. It changed everything. She could finally keep up, could finally go on the rides she missed out on, and she had such a great time. We continued to rent for the remainder of that trip, but one time (I think MK) they were out of scooters and that was tough for her again. We now rent from off-site places so she can use it at the hotel and parking lots too. It's a total game changer.
In 2016 after her cancer surgery, she lost about 100 lbs, maybe more. Still has asthma and COPD, so still has the breathing issue, so she still rents the scooter and she wouldn't do WDW any other way now. She still qualifies for the
DAS (at least she did in June 2021) because of the COPD. Forgive me for asking, but does your dad have an actual named back condition, something with a diagnosis, something a doctor labeled as a condition or disease? I'm not up to date since this past summer with the
Genie+ changes, but I'm curious if that's what disqualifies him for DAS, the fact that there's no labeled name to his condition, just "sore back" doesn't cut it for their qualifications anymore? I wonder if you said he has degenerative disc disease, or some such, if he would then qualify? Again, I don't know how it's changed since Genie+ is now involved, so I apologize for my lack of knowledge here.
I highly recommend you keep pestering and nagging him to just try it. Try. See if he'll give in to just one day of it and if it's too embarrassing, he still has too much pride, then fine. You gave it a shot, and thank him for that. It made such a huge difference for my mom, I think it would help your dad too. Good luck.