From my limited SP-experience (as opposed to the probably much richer MP-experience some players possess) the issue with naval invasions in 3 was not about the number of provinces or ports - i think those are pretty decent. Okay, there could be landing-suiability ratings for all coasts, making it easier to land on the beaches of normandy than at the cliff of dover, but i am fully aware, that this would have meant a) 5€ extra for a game coming out one month later and b) possibly UI/map-clutter.
No, the issue is that loading and unloading in ports takes zero time and carries no other penalty (like, say, a ORG-hit), either. It´s like the tanks roll right onto ferries waiting in (tank-)formation at the shore, which go over the sea with perfect navigation against all wind and currents, to land on the other side in exactly the same perfect formation, and everything is timed perfectly, so that when the whole unit is back on land, nobody had to wait for anything or anyone and the whole thing just rolls out again in perfect formation, even if the enemy is already attacking the province and the port is currently being bombed...
The dis-/embarking without ports was carried a big way towards getting fixed in tfh, but still some issues remain with those as well. Like it always takes the same amount of time to do it (right?), no matter what the weather is like or what´s going on on land, in the air or at sea. But the warning an invasion has been started and the delay caused by modeling the process of disembarkment were heading in the right direction.