Overture is a data-centric map project, not a community of individual map editors. Therefore, Overture is intended to be complementary to OSM. We combine OSM with other sources to produce new open map data sets. Overture data will be available for use by the OpenStreetMap community under compatible open data licenses. Overture members are encouraged to contribute to OSM directly.
I don't know a lot about any of both projects, but it seems fair.
It seems they consider themselves complimentary with OpenStreetMap, as stated on their FAQ https://overturemaps.org/resources/faq/#
I don't know a lot about any of both projects, but it seems fair.