Everything in my house vents into the ceiling cavity. Should I change this?
In an apartment building they may have deliberately designed that area to function as a plenum space. That design would -- one hopes -- include selecting/arranging building materials that could tolerate the moisture these fans would pump into that zone.

In your house, it's less likely that folks made the appropriate effort.

Rot isn't the only issue. At best, more moisture in your insulation will mean it insulates less well than it should. I don't know enough to have any valid opinion on whether the fact that you have the spinners to help actively encourage airflow will make up for that.

Personally, I'd say either fix these to exhaust to outside, or at least spend a bit of money to get an expert opinion on whether you can get away with not doing so.

(One of my bathroom vents exhausted into the attic. My inspector, an old-timer, grumbled but didn't actively recommend fixing it. My insulation contractor took one look at it and said "I'm fixing this.")