While I generally believe a round 4 Sealion is unstoppable, my question is if the Allies can set themselves up in such a way as to sink the German fleet after a G4 Sealion? If that is possible, then maybe the thought exercise in this thread isn’t so futile.
In my limited opinion on the topic of sinking a G4 Sealion fleet, I keep coming back to the point that it is on round two that the Allies must begin purchases in order to do this. If this is the case, and Germany sees the Allies prepare for this possibility, why would they do a G4 Sealion? It would either be a G3 Sealion (which may not have what I consider great odds) or skip it and go Barbarossa with their large fleet.
Of course, these are just my thoughts on the topic.