how's the AI (as in computer opponent) these days? last time I played vcmi, that was my only gripe – the bots were so stupid.

They're still not too bright, which is kind of faithful to the original game. However at least the android client allows you to pick alternate algos and further AI mods that at least claim to make it more challenging are available for download.

There's an ongoing project of build an RL AI https://github.com/smanolloff/vcmi-gym/