I get your point. Spain would fail miserably.

But you’re not taken into account how many men Russia is losing to maintain that level of aggression. It’s compensating its small GDP with humans.

Spain would never do that and thus fail.

Actually yes. Ukraine is far easier to invade for Russia. Geography is super flat. You can drive in from anywhere. Easy to supply thanks to sovjet rail. Spain is very mountainous and a pain in the ass to invade. How would Russia supply their troops that are completely rail dependent?