How do we know we aren't playing against bots

As said, that’s not surprising — I’ve commented on their poor documentation many times [1-3].

Yeah, I remember. I got into PvP a bit later, and I don’t think you would meet bots (that is, the aforementioned AI opponents; botters, though, are a different matter) then, even on low ratings.

[1] 24.0 Patch Notes - #23 by SparkyElf-2852
[2] 25.0 Patch Notes - #27 by SparkyElf-2852
[3] 25.0.3 Patch Notes - #26 by SparkyElf-2852