If however I was a frontier lab who solved continual learning and my competitor also solved and released it, I would release mine immediately, obviously.

The point is, continual learning might be solved already, we just don't know and those who might know would rather keep their mouths shut. It isn't my base case (financial situation of frontier labs is such that they'd probably release immediately as long as they have inference compute to serve this revolutionary capability), but it isn't impossible.