22 characters is significantly less useful than 255 characters.

You can still use more than 22 characters; it just switches to the heap.

nothing I am going to store is ever going to require heap allocations

I would put good money that using 256 bytes everywhere is going to be slower overall than just using the heap when you need more than 22 characters. 22 is quite a lot, especially for keys. ThisReallyLongKey is still only 17.