Actually, no. The decentralization of power means that it takes a lot more effort to subvert each country individually, rather than propping up a few candidates for the entire region like they do in the US.

No because any attempt at interference would in that case trigger article 5 of NATO.

That’s true but that fragmentation is also what limits the propagation of fractures. You can see it like sandboxing.

A deal with foreign intelligence is a dead with the devil that comes with a lifetime of subservience. And subservience to foreign powers is a greater evil than yo usual internal corruption. At least the locally corrupt in a democracy have some interest in things going somewhat well in their country. The foreign actors only care about theirs.