I live in a small five apartment building. Two flats were remodelled at the beginning of 2020 for airbnb. That did not work out because of covid. The owner of one flat then decided to live there herself and she is a nice neighbor (the other flat is still empty).
What evidence is there that people in "some metropolises have less interest in interacting with their neighbours than decades ago"? I can't speak for Helsinki but honestly the behavior you describe sounds borderline pathological. I've lived in many cities around the world and would not describe that as common.
That's what "zoning" is for.
Maybe the city should just designate a zone / neighborhood for short term rentals and call it a day.
I understand the "decentralized hotel" problem. But, this seems to come up with fiery enthusiasm in the context of housing affordability constantly. Ultimately, affordability is a bigger problem then neighborhood character.
No one gets this fired up about sidewalks, business licensing, speed limits, parking and everything else that makes up neighborhood character.