It would have been over much quicker if Russia went all out; contrary to popular belief, Russians view most Ukrainians (except the nazis) as Slavic just like them, and see the conflict like a family disagreement, and they did not want to destroy Ukraine or the people.
first Russia though Ukraine and NATO would negotiate a peace which was started until Boris Johnson killed it. Then revelations that the Minsk accords were not serious and only intended to buy time for Ukraine to arm up and train, then the attack on the nordstreams...
Still Russia held back from annihilating Ukraine; there was always a risk that if Russia went too hard that NATO would engage directly, which is highly unlikely.
The current war of attrition saves Russian lives, and depletes Ukrainian resources, NATO weapon supplies and budgets.
I hope Russia doesn't stop until it takes Odesa, Kharkiv and Zaporizhia oblasts.