It is extremely technically difficult to make jetliners be "roll on, roll of" for power chairs. That is not likely to become possible to improve anytime soon, and it is why airlines are exempt from ADA.
Take the train
Amtrak is subsidized for a number of policy reasons. One is to enhance accessibility for folks like you.
If your location is Buffalo, you have reasonably good access to the national system. Pennsylvania and West Virginia are hard, but you have decent access to the East Coast and South, and the west is your oyster. In particular, going from Buffalo to Los Angeles,
you would be on the Lake Shore Limited, the east's fastest overnight train. Midnight departure out of Buffalo, sleep through northern Ohio, and a 9am arrival in Chicago. Spend the day shopping (you're blocks from the Loop).
Then a 3pm departure on the Southwest Chief, the fastest overnight train nationwide. It uses a mountain-avoiding straight-shot on the "Santa Fe Racetrack" route, so it is much faster than the southern, central or northern routes. The 43 hour night-day-night run puts you into L.A. between 8am and noon.
Accomodations exist both in coach and sleepers. The eastern trains have a high deck, and use either high or low level platforms. At low level platforms, they will use a "wheelchair lift" to get you to deck level. The corridors are too narrow to reach the whole car, but you will be able to get to the ADA sleeper compartment or a chair tiedown area in the coach, and a bathroom.
The western trains (and Auto Train, and Capitol Limited) use low-deck Superliners, which all use low-level platforms and a very simple ramp. You will be able to move about the lower deck of the car somewhat. The attendants will bring you diner meals or snacks from the cafe car.
In sleeper cars, dining car meals are included. Coach passengers can pay for dining car meals a-la-carte. Both can buy 7-11-tier microwave fare from the cafe car. The cafe is priced a bit above 7-11 and far below airlines. The dining car is priced like Applebee's.
Let me give you the standard speech about late running that I've been giving for 25 years. A very, very long train run has many opportunities for small delays, and all those delays stack because Amtrak doesn't build much recovery (sitting around) time into their schedule. You just have to plan for it, relax, and don't worry about it. If you can't settle for that, then
Amtrak is not for you clearly, you haven't flown much in the last 10 years...
I travel Amtrak a lot, and have seen some whopping delays for wild (but reasonable) reasons. My worst, however, was actually on JetBlue.
In my experience, Amtrak often tries to work alternate transport during long delays. When there's a viable choice, I find it's usually wisest to stay with the train and wait it out. The railroads are very, very good at keeping their track open, and Amtrak trains are modular and single broken engines or coaches can be set out or simply carried along inoperative.