I have a big and a quick blog post in preparation, but both are calling for a preceding one to explain a particular assertion of mine in greater detail:
First, let's agree that air power can destroy surface ship targets very well if suitable hardware and training is available (especially enough munitions) and the range isn't too great.
Surface warships would engage other surface warships primarily with quite lightweight surface-to air missiles (against which hard kill defence are quite impractical) and usually dedicated anti-ship missiles (of which usually no more than eight are on board).
Combat aircraft meanwhile would typically use supersonic anti-radar missiles and anti-ship missiles (quite the same as fired by surface warships) in synchronised attacks, and follow up with bombs to finish off the already damaged ships. This air power can be shifted by hundreds of kilometres within less than an hour. Surface warships of any kind - including dedicated air defence frigates, destroyers and cruisers - without benefit of support by fighters and AEW aircraft would be little more than snail-like targets; easily stomped one after another by air power.
That air support is hardly going to be reliable.
So essentially, the Eastern Baltic Sea and much of the Black Sea would be at least very, very dangerous waters in the event of war there. This suffices to make the sea lanes through these seas unacceptable for maritime transport in wartime. One could try to force one's way through such dangerous waters, but the outcome would be unpredictable and thus unreliable. If nothing else, the threat of air attack, missile attack and maybe even artillery to the ports in the region would disqualify the sea lanes.
It would be irresponsible to allocate resources to such maritime activities when it comes to designing the national military of the 2025-2030 period. Thus we should not plan to use these seas in the event of collective defence.
Similarly, there's hardly any - if any - justification for spending on naval abilities to kill hostile warships in these sea areas. This would de facto be all about modern submarines (SSI) anyway, and those are very specialised ship killers with hardly any relevance to air or land warfare. Yes, they could also launch land attack cruise missiles, but so could a barge - and the encapsulated cruise missiles for launch from submarines tend to cost twice as much per copy than those meant for surface launch.
The spending for ship-killing capability in regard to such seas should be about air attack and anti-submarine mining in narrow straits (Bosporus, Øresund et cetera).
Summarizing this, I say we need no navy in the Eastern Baltic Sea, we need no navy in the Black Sea, and whatever aggressor naval power might be there in the event of collective defence would merely be a diversion for our air power, keeping a couple dozen combat aircraft and up to twice as many crews busy for a few days.
Now the other part of the story; what if an aggressor (Russia, of course - the only not entirely unrealistic threat) has fleets there despite them sitting in a death trap?
Typically, this would lead to primitive reactions; every ally of ours with a port in the region would feel compelled to maintain a navy. Typically the urge would call for a well-rounded navy. A few subs, a few air defence ships, anti-submarine ships, mine hunters...a huge waste of funds.
This makes hardly any sense, for said threat fleet would be useless there in the event of war. The surface warships would be little more than targets for air attacks, and their submarines would not find targets unless we're stupid enough to feed them. Whatever cruise missiles the threat fleet could launch could be launched in the first five minutes of hot conflict, so it would be irrational nonsense to spend funds in pursuit of an ability to kill the platforms before they launch cruise missiles.
Those threat fleets become troublesome only if they leave those restricted waters prior to conflict and reach the Atlantic Ocean where air attack would be much more difficult due to the distances involved.
Now should those countries in geographic proximity to the only relevant land and air power threat build fleets that could follow a fleet into the Atlantic Ocean and engage it there? I suppose that would be nonsense.
Their geographic situation demands a focus on land power, and (only if the budget is large enough) secondarily air power. There are other, more distant, countries which are obsessed about naval affairs because of irrelevant irrational reasons such as past naval power or the length of their coastline. Those will afford the naval power needed to subdue a timely evacuated threat fleet, regardless of what a country such as for example Romania does in regard to naval spending.
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I mean no offense, but I do not expect readers / commenters to fully follow this post and to absorb the reasoning. It's too distant from mainstream for this. There are plenty special interest groups that push the other way as well. Still, I felt this separate elaboration was appropriate ahead of the coming blog posts.
Long story short; our European deterrence and defence would not suffer if less (or nothing) was spent on naval power in the Baltic Sea and Black Sea. To some extent the musings above can be applied to naval power in the Mediterranean Sea as well.