Right. That is legal for a FRIENDLY landing, but not an amphibious assault.
And it is true that aircraft operating alone get to fire on enemy SUBs ONCE before the SUB can submerge (in revised anyway).
Personally, I think that the SUB should be able to do its opening fire step as a “submerge” against an air only attack. At a bare minimum, allow the SUB to roll its “to hot” die, and if they hit, they submerge before the aircraft could attack them.
Historically, SUBs were killed by DSTs, not aircraft. Aircraft inflicted SUB casualties were pretty low for most of the war for all sides.