I wish I'd had better experience with other tablets. I have two and they suck. But my Fire tablets all still run really, really well (I have 3 that I actually use - 6" HD, a 7" second gen, and one of the cheap $50 Fires). Netflix and Prime video play great on all of them and I don't have any problems with books or storage. My *other* android tablets are pathetic--slow and unresponsive to the point of making me want to pitch them across the room.
But I hate the fact that I'm stuck with just Amazon stuff on the Fires. So there's that.
I have a 128 gb card in my newest fire and store my entire Calibre library of 2000+ books on it, synced with Calibre Companion) and use Aldiko premium to read them (both of those apps are from the Amazon app store). I have the same library on my oldest second gen Fire which has no external storage at all and it works just as well. I'm actually kind of amazed by that every time I sync it with my library and read something on it. It's still my favorite.
I probably need to buy a high end tablet if I want to get away from Fires, because the low end? They're so much worse. I wouldn't suggest anyone try a low-end android tablet hoping for something better than a Fire.
As a temporary solution, I suggest a factory reset so you can get a fresh start while you take your time finding a good quality replacement.