TFA focuses on cost, not energy use. A mini-split is a lot more efficient and doesn’t leak air, and it’s a lot quieter. Better yet, water to water heat pumps could be used to retrofit the existing steam systems.

but the landlords won’t do it

Not without incentives, you’re right. Update the building codes already.

FTFA:

because heat pumps move heat instead of creating it, they can be three to four times more efficient than traditional heaters

Air to air isn’t that efficient. I wish.

Transitioning to window units in apartments could also change who pays for heat. In apartment buildings with centralized heat, landlords typically cover that cost, Nadel said. But if you switch to window heat pumps, the cost of electricity to run the units would probably go on the tenant meter. “Hopefully the landlords would cut the rent proportionally, so that this extra cost doesn’t get moved to the tenant,” Nadel said.

Well, that’ll make the landlords excited about distributing window AC everywhere.