I think you are basing your reasoning on a few mistaken assumptions.
First, there is absolutly no equivalency between the Crimea -or Ukraine- and a NATO member. Ukraine is a European country that the west would quite like to see as a western, prosperous democracy. But it is not an alliance member. NATO is a defensive alliance designed to protect member states. NATO isn’t really in the business of going to war over non-members.
Also, the west isn’t really going to start a war over something they’d quite like.
An attack on a NATO member, however, would be an entirely different issue. If NATO doesn’t go to war over that, NATO is over. And NATO countries would rather have a war now, all together, than a war later one on one.
So Ukraine =/= a NATO member. Marching into Ukraine =/= marching into a NATO state. Big, big, big difference.
Second, Russia isn’t really powerful in terms of their conventional military. Not compared to NATO, just the US, or just the EU. Russias military budget over the last decade hasn’t been much bigger than the UKs, or Frances. Russia has a big army and a lot of handmedown equipment from the Soviet Union, which has gone through decades of being poorly maintained.
Yes, Russia is big and powerful compared to Hungary, or Slovakia or the Ukraine. But the EU has more than three times the population, and Russia basically has a military budget slightly larger than Britains, and an economy only slightly larger than Italys. And then you have the US…Which is heavily dependent on the EU as a customer.
So Russia =/= the Soviet Union in power.
Third, the US is quite fond of its credibility as a treaty partner, and the other NATO countries would much rather all pile up on Russia together, than fight it separatly down the line.
Finally, don’t confuse a high threshold for going to war with a lack of resolve about it. Europes history involves a lot of wars between equals, which tends to be very different from the “war as a spectator sport” the US is used to. So Europeans have a much higher threshold about war, but go to it with the understanding that it involves stuff like 9/11 happening daily.