OpenStreetMap's platform is the only real way to compete against Google and Apple and it's why Microsoft even though it has Bing Maps, has licenced to them resources like satellite imagery for mapping. It's awesome in bigger population areas but there's still a lot to map in rural places outside the EU.
Review is harder. Right now the leading open platform afaik is Open Reviews (aka Mangrove Reviews) which has tie-ins to OSM projects like MapComplete. OsmAnd and OrganicMaps have open tickets to hook into that ecosystem. You're right about the userbase problem though, I think it (or a successor) needs AP federation to really take off. That being said there's several active non-Google nonfree alternatives like Yelp and TripAdvisor as well as niche sites for things like camping, parks, and schools.