I think we're ultimately seeing a failure of the combat system in which you pay no penalty for, and labor under no limit of, the total number of units you can stack in any geographic area.
Its not just at sea either, you see the same thing in the air war or on land.
One really big stack of troops in one province, backed by a single division in each other border province ends up being the near optimal land deployment, especially against an opponent who distributes his forces in a broad front strategy. Your uber stack can just chew up his army, one province and fraction at a time.
One really big stack of 24 bombers and fighters ends up being far more useful than 4 stacks of six. It suffers proportionately less damage to ground fire, fights off intercepting fighters better, and does more damage to boot.
The problem is most apparent in the naval world, of course, becasue there's really no penalty for *not* having ships in, say, the north sea. Meaning if you want to put your entire navy in one big stack and sail it off to fight the japanese, there's no single italian cruiser running around "conquering" the ocean.
Until HOI introduces some form of either a stacking limit or reintroduces the old EU 2 attrition model, the issue is going to persist, and introducing either of those will result in a *huge* effective nerf of the USSR which will no longer be able to count on outnumbering the germans at the point of decision.