The trust deficit is so low with the West, the Russians can't do a deal with them. If Ukraine agrees to 'neutrality', what is to stop them from reneging on the deal later? The deal has to be bilateral only, and in a verifiable manner.
Lavrov has said before that the US is a disruptive influence in the negotiations.The US has basically stated that this will be a long war, and the end is regime change in moscow.
Ukraine doesn't need donbass, but that doesn't mean it should be handed over to Putin either. If they want to be independent within Ukraine, that is an option. After a referendum that is overseen by the UN of course. But it should never be handed over.