So why even have conventional forces then?
Your question appears to miss the point.
I say Russia is a threat to more than just Ukraine.
Opponents say no, most other nations there have NATO. Russia wouldn't risk it.
To which I reply... risk what? Not nuclear war. That we will all choose to engage in conventional war is entirely my point. The illusion of the nuclear shield is gone, WAR is back on the menu.
I posit that nuclear nations WILL NOT commit to MAD for someone else's sake. Russia is poised to call our bluff and attack NATO countries. Not this year, maybe not next year either. But it will be something we slide into from here UNLESS Ukraine can hold. I also posit that Crimea is the key to a secure Ukraine, thereby avoiding future conflict with Russia. But if Russia keeps the land bridge, and its forward base... Kyiv is at real risk of falling unless Ukraine can secure the Black Sea and its southern flank.
We cannot afford to let Ukraine's offensive power falter until the goal of Ukraine's security is achieved.