Let's put that hardware stuff aside for now, and talk about software:
The Kindle Fire is Android, but with Amazon's apps and modifications. That's common in the Android world. For example, a Samsung tablet (including smartphones) will have Sumsung's apps and modifications. Now, it's true that Amazon doesn't market Kindle Fires as Android tablets. There's a good reason for that: When people hear "Android", they'll think it has the Google app store and Google apps. The Fire doesn't (unlike even most modified Android systems), but you can install them yourself.
So Android vs Fire: That's the wrong question. The right question is: Near-stock Android vs a more modified Android. I've never used a near-stock Android. But I've used two Android systems with very different types of modifications. One is a Kindle Fire, the other is Chromium OS (aka Chrome OS, Chromebook) with Android app support. Originally, Android and Chromium OS were originally totally separate projects. Now, Chromebooks with Android app support
are pretty much Android by another name (although some Chromebooks don't have Android app support).
You might think that, with two different flavors of modified Android (or modified to be Android in Chromium OS's case), I'd have two very different experiences. But I haven't. Ture, there's some work to get them close enough to stock Android for my needs. I had to install the Google appstore onto my Fire, along with basic Google apps which would normally come pre-installed. I had to activate the Android sub-system on my Chromebook (which itself is using a modified Chromium OS). But after the work I put in, it's pretty much the same experience.
Of course, there are caveats when using such a far-from-sock Android. I've already told you one caveat: The work I've put into getting both systems close enough to stock Android for my needs. The second caveat is: Not everything's going to work as smovly as it would under a near-stock Android! For example, I've read that the Kindle Fire doesn't work too well with custom launchers. I myself haven't been able to get custom keyboards to work properly with my Chromebook.
You may want to avoid that risk and headache, and stick to a near-stock Android. How can you find a tablet with a near-stock Android? I don't know. But if you'd like, I could look into that for you.