Finland first proved itself a very hard nut to crack. Stalin settled for relatively small changes to borders, much less than Putin achieved in 2014, let alone what he's trying for now, & Finnish neutrality. He imposed limits on some categories of weapons for Finland, but not on numbers of troops (Finland adopted something like the Swiss model of national defence: a nation in arms, but without offensive capability), & let the Finns choose their own governments.Correct, but consider the position that was taken. The country itself gets to decide? Clearly there's more to it than that.
I don't think that's necessarily true. Finland faced similar issues during the Cold War but they didn't end up a Soviet vassal state, and it wasn't their military power that prevented it. WWII analogies are popular but I don't think they fit here, the situation is just too different. In general I think that Ukraine needs security guarantees from the west and economic development. If they get both, and they're credible, they can maintain a small domestic military. If they don't, a large military will still face ultimate defeat. And of course the cost of continuing fighting is making future defense more difficult. A Ukraine with 35mln population and a decent amount of western investment could become quite strong. A Ukraine with 15mln population, and crumbling infrastructure could be easy pickings. The best defense to Russian expansionism is a firm, economically successful, and politically stable Ukraine. An impoverished, smaller Ukraine militarized with western aid, but economically in poor shape is a recipe for a continuation war.
Putin seems unwilling to make peace on anything like those terms.