Tenancy is a contractual relationship. It doesn't include ethical sidequests like making sure your landlord doesn't pay large electrical bills which he has agreed to pay as part of the contract. Electricity is metered, making it the landlord's responsibility to put an "up to X KW a month" clause in the contract. That electricity isn't free, the scare quotes don't change that. It's cost-included.

Your opprobrium appears to hinge on the idea that this tenant would only mine crypto if the power is provided on a single-bill, all-you-can-eat basis, which I don't see as a safe assumption here. The tenant got a good deal. That happens sometimes. If landlord ever notices, he'll put another clause in the contracts going forward. Live and learn.

I wonder how running several computers would compare to other high-current draws that we would consider normal use, like using an electric oven a lot (3kw, plausibly 10 computers).

The oven won't be on 24/7 and even if you're baking the elements cycle on and off (that's why you hear the clicking relays). You'll have to integrate it over a month and compare that to the constant consumption of a mining rig.