They aren't planning to use 42,000 Starlink 2 satellites.

The current plan is to deploy 10K to 30K satellites. They don't think they will actually need 40K.

Furthermore, the majority of their satellites are first generation, which weigh only 250 kg. They are only authorized to launch 7000 Starlink 2s. Starlink 2 satellites are more capable, so every Starlink 2 they launch will reduce the total number needed.

SpaceX launches 10 or so Falcon 9s a month. Each one can carry 60 of the smaller satellites, but only a handful of the Starlink 2. I don't think it's feasible for them to launch an average of 23 Starlink 2 satellites a day, even after switching to their bigger Starship rocket. And what comes down must go up.