Agreed, and even if Russia was "content" to "only" take the territory they currently have occupied, and Putin could somehow sell this to his population as a "victory" ... the long term situation would be a nightmare.
They would not stop undermining the independence of Ukraine, and would in fact be emboldened to do more. There would be no "peace", there'd be hybrid warfare incursions constantly, they'd start crowing about Russian language rights even more, and use it as a justification for meddling probably at an even more intense level than before. Every election would be undermined, people assassinated, bought off, manipulated.
Remember Russia last year changed its constitution to include Ukrainian land in its borders. Lands which it currently doesn't even occupy.
They have spent the last 10 years selling their population on the line that Ukrainians were doing some sort of genocide on the population in the Donbas -- so just imagine if Donetsk and Luhansk oblasts were split in two, as they are now?
Official Russian ideology is Russo-supremacist, with an Orthodox Christian nationalist veneer. This is not the USSR era, with its "brotherhood of peoples" propaganda. Its right wing nationalist, and imperialist on that basis, and has shown itself willing to attempt to enforce this.
Eventually they'd either get their way and turn Ukraine back into a client state, or invade again.
Russia needs to be pushed back, its defense lines broken and its trade relationships properly severed, its energy exports denied access to the west until a substantial foreign policy shift is made by its leadership.
Oh, and removed from the UN security council or the security council just abolished.