Russian fortifications present an old problem for Ukraine
engelsbergideas.com
engelsbergideas.com
I don't really see why the West would be bothered by a long drawn out conflict. I think the other superpowers felt more relaxed when the US was properly tied up in Afghanistan, a defeat and withdrawal makes them much less predictable.
Having a direct flank open to NATO troops at any time, regardless of why they might be on the march, was always a strategic problem no matter what. It was less of a problem when such troops where a couple of borders away; it is a pretty big issue today. They tried to address it with the dirty war in Donbass, but clearly it wasn't going as well as they hoped. Putin just decided to try and cut the knot.
Ironically though, by trying to claim the whole country and failing, he created a self-fulfilling prophecy. Before this, there was very little realistic chance of Ukraine ever joining NATO, nobody in the alliance wanted them in (not even Eastern countries for which it would be a useful buffer: they would lose the relevancy they get by being "the border"). Now, if they manage to maintain statehood by the end of this conflict, it will be politically difficult to keep them out.
> Russia had no reason for Crimea other than their naval base
That naval base is a key element of force-projection for Russia since boats had sails. They fought multiple wars for it and will not renounce it, short of catastrophic humiliation on the battlefield - something that today would probably involve exchanging nukes.
Ukraine probably doesn't want anti-ship missiles. They would prefer cruise missiles like Storm Shadow for attacking ground targets. They also make their own Neptune anti-ship missile for defense. Plus, Sevastopol is heavily defended, Ukraine has avoided saturation attacks and makes more effective smaller attacks. They have lots of more important targets.
Finally, the west doesn't want to escalate the conflict with Russia. Most of the Black Sea Fleet is hiding in Crimea or Russia. If Crimea is too dangerous, they can retreat to Novorossiysk.