The problem is, however, the longevity of these batteries. In the smartphone world, we've seen a huge emphasis on "50% charge in 10 seconds" but I like to believe batteries weren't designed with that in mind.

I refuse to use 'fast charging' since I believe it will reduce the life span of the battery (which I guess is what they want so you buy a new phone).

If it can be proven batteries can charge much faster AND have an acceptable life span, that's okay. But I don't think that's going to happen any time soon.