What’s the point though? To save prospective renters time?

I’ve lived here for 30+ years, rented for more than 20 and why would anyone ever rent an apartment without seeing it in person?

That being said, IANAL but I imagine the rule is fully legal. The city already mandates a host of things: if the listing markets something as a 3BR, it needs to have 3 rooms bigger than 80 sq feet, each with an exterior window. If they say 3BR and it needs a wall to created the 3rd BR they have to put it up. If it says 2BR convertible 3BR, you might have to pay to have it put up.