Setting aside ideological purity, the actual rationality of switching solely to OSM depends on the actual quality and freshness of its data. And most of the world with money in play is more likely to follow rationality than ideological purity here.
But with regard to data quality, OSM is encumbered its own policy. OSM cannot (or refuses to) make use of high-quality bulk data from outside, regardless of how that data was licensed. Automation allows more frequent updates with a lot less manual labor as input - but OSM requires contributors to manually trace shapes in their weird browser app. Even where plenty of excellent liberally licensed data is available, OSM insists on making an army of unpaid monkeys re-make the SAME data in perpetuity.
That puts its pipeline at a permanent disadvantage to companies building proprietary datasets, which can take advantage of all kinds of automation. OSM simply isn't doing as much as it could to verify its data and stay fresh, and so it isn't doing as much as it could to end the status quo of proprietary data. Even if OSM reaches a usable state at a given moment, the world keeps changing to invalidate previously traced data, and OSM's policy ensures it will always be playing catch-up no matter who wants to donate data, because all the data has to come through this dopey manual process.