Well, federated platforms seem to have avoided it, since one actor can't just degrade the quality of the whole service. See for example, the Fediverse in general.
Fan/individual/community run sites and networks seem to avoid this issue, since they don't need to make a profit from their work/pay off those venture capital investments. For example, the Nintendo Independent Wiki Alliance seems pretty good there, with the likes of Mario Wiki, Zelda Wiki and Bulbapedia most relying on unintrusive advertising to stay afloat.
For a well known platform? I guess WordPress.com seems pretty good in that respect, at least from the sites I've visited there. Can't see many ads, paywalls or other dubious practices there.
