So, the big question that makes this whole discussion moot is: What does building navy in the Baltic actually -do-? What is the goal of building it?
1. It ferries a few additional troops to Karelia faster.
Ok, but taking and holding the Karelia factory accomplishes the same purpose without wasting IPCs on building navy. In any case, the land units you build in Germany will get to the eastern front eventually, whether by walking there or taking a transport. Does a few of them getting there slightly faster until the navy dies accomplish that much (i.e., is there a quick attack that kills Russia very fast where you need those few extra troops in the east a couple of turns earlier)? Nah. The game designers were smart enough to make sure there’s no cute tactics like that which Germany can pull - it takes at least 6 turns or so to really take Moscow against any sort of decent Russian player, and the Baltic fleet should be dead long before then if you don’t play the naval arms war with England more than a carrier or two.
2. It threatens the UK with invasion.
There is no way that Germany can build enough of a navy to compete with the UK -and- hold the east against Russia. It’s just not possible with the IPCs that Germany has access to in the beginning of the game. So, one or the other will have to go. Besides, the UK can easily build enough land units to prevent Germany from ever really taking the UK. US can come with assist if it’s ever needed, but it won’t. So this threat is empty in that it doesn’t gain any territories for Germany, and they’ll be losing territories to Russia while sitting around building this empty threat.
3. It makes the UK focus on fleet for an extra turn or two instead of prepping invasion of France or Scandinavia.
Ok, but it also makes Germany focus on building ships instead of land/air units, like they should be. So this is a trade-off, and one that Axis can’t really afford to make IMO. UK will eventually crush the Baltic fleet, and by crush I mean not a fair battle. Axis will lose on the IPC trade and UK should be left with a fleet that is unassailable, and -then- they can start the invasion prep. Also, by building ships, Germany is going to start losing instead of gaining land IPCs to Russia as they begin losing the land arms race since they are preoccupied with ship building.
So, I think we’re left with admitting that building ships as Germany has no real goal to it, and therefore, it’s a bad move. Whether it’s a lone carrier, or something more substantive, those Baltic ships that Germany builds will either sit there useless, or get destroyed, and you’ll wish you had spent those IPCs on something else, like maybe inf/arm/fig/bmb.