one nuke would have been quicker and cheaper.
Yeah, but that is an escalation which would first, not provide a testing ground for Russian conventional weapons systems and upgrades, and second, crosses a threshold that has remained since WWII. Once crossed, the genie is out of the bottle, and the use of Nuclear weapons in retaliation against not only Russia, but the Western Powers becomes a real possibility, as soon as such can be developed or deployed.
It is one thing to have a rollicking fistfight, but the nature of the fight changes when someone pulls a knife or fires a shot.
So far, this is just shaping up to be a slugfest as far as countries go, even if the sides don't seem even, and don't fight the same.