Kuwait '91ing all of Putin's forces inside of Ukraine does not necessitate a nuclear showdown, and deterrence works both ways. Did we end up in a "nuclear showdown" when we wasted 400 Russian Vagner mercs in Syria? No. You can have conventional conflict between two nuclear-armed powers without any such "nuclear showdowns" ever taking place--see Pakistan & India constantly shooting it out over Kashmir among other areas.

How many other bloodthirsty dictators are going to be clammering to get their hands on nuclear weapons once Putin has showed the world exactly what one can get away with simply for possessing nukes? The risk-aversion for conventional conflict against a nuclear-armed actor is going to do *wonders* for nuclear proliferation in the future, and it will be because we incentivized it today, here, now. When the next guy who is less-rational than Putin gets a new nuclear arms program, it'll be because we showed them how scared we were today, remember that.