On war 273: "Defending the Baltics", by William S. Lind
I've heard similar opinions before, since the Russians fought in Georgia.
An insurgency as defensive strategy, to defend against a superior power.
That's folly in a situation like the Baltic states' ones, for it is a very poor Plan A. It can be used as Plan B, but even then it's a bad idea.
The Baltics already had an insurgency against Moscow's rule, the last insurgents ceased their activity sometime in 1952 after many years of occupation. The Baltic states have only a very small population each, and therefore little power even in an insurgency.
Stalin deported great parts of opposing nations (Chechens, Ingushs, about 10% of the Baltic population) to handle rebellions and Putin flooded Chechnya with more military and para-military personnel than Chechnya had inhabitants, just to crush the insurgency there.
Insurgency does not work out well against Russia. The Russians don't apply the same self-inhibitions as Western powers in insurgency, and defeat rebellions. Their costs are high, but not so high that the prospect of an insurgency could reliably prevent an invasion.
Lind is also wrong on his "toy army" argument. A conventional all-round army/navy/air force design is unsuitable as he wrote, but that does not exclude the possibility of a conventional warfare defense.
Those states cannot defend themselves against Russia, but they could delay an invading force if well-prepared to do so - this capability could offer sufficient deterrence in conjunction with credible reinforcement preparations by their NATO allies.
Some people over-estimate insurgency / 4th Generation Warfare decidedly, and belittle the utility of conventional military power.