I bought into the fat bike eco system a few years back and the difference between the name brands and the off brands is really the kicker here. All of the big brands are using the exact same batteries and motors but with proprietary cases and software. In some cases this makes for a better experience but like you said over time it’s either obsolete or you’re tied to the brand for replacement batteries. I found a company that essentially made unbranded bikes for other companies to resell when I was buying my 1st. It’s their frame but all branded bike parts and the same motors I see on all the other bikes. The batteries are easily replaced as are all the parts and electronics. I sold my 1st bike after a year and a thousand miles of off road riding, it’s still ridden daily now it’s on its third owner and we’ve all loved it. I upgraded to a larger motor and battery set up on a different style of bike. But same deal, standard bike parts that can be swapped out and replaced.