> The interesting and difficult thing to process here is whether this is a provocation without turning it into 'whatabboutism'
I don't know what you mean with whataboutism in this context, but traditionally non-allied European countries considering their defensive options when Russia has invaded a sovereign nation is certainly not a provocation.
> Joining NATO means millitary bases
Not automatically. Not all NATO member countries have e.g. American military bases [1]. The Baltic countries have a small NATO military presence, but not a large enough one that it could pose any offensive threat towards Russia.
It's entirely possible for a NATO member country to say "no thanks" to foreign military bases. That might even be likely at least in case of Finland which has maintained its own credible defensive capability.
If Sweden or Finland consider joining NATO, it's because they'd like to have someone's back in case of a crisis, not because they'd want to host someone else's offensive capability.
> troop exercises
All military forces conduct exercises.
> and 'defensive' missile installations that can be easily converted to offensive missiles without any visibility
Again, that's up to the individual member countries. Also, I'm not an expert on missile tech, but I don't think e.g. anti-air missiles can be easily turned into cruise missiles or other kinds of offensive weapons.
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Russia would likely consider Sweden or Finland joining NATO as a provocation. But it's not really possible in good faith to believe it would actually be one.
[1] https://en.wikipedia.org/wiki/List_of_United_States_military...