I don't think a single satellite can saturate a cell, but I think you're right on a couple gateways being able to soak up a couple beams from multiple birds. That might work on rare trans-oceanic cruises. But for the most-common routes, which nose along coastlines, there are other beam uses.
https://mikepuchol.com/modeling-starlink-capacity-843b2387f5...
Beams are 250MHz wide and they have 2GHz of allocation.
I don't think a single satellite can saturate a cell, but I think you're right on a couple gateways being able to soak up a couple beams from multiple birds. That might work on rare trans-oceanic cruises. But for the most-common routes, which nose along coastlines, there are other beam uses.