EDIT: Anyone interested in this topic, search YouTube for Norther European Plain. There are quite a few good videos.
If you meant neutralized in the military sense (combat ineffective) I agree.
If you meant politically (seeing as you wrote 'friendly' for Belarus): Ah yes, when I get kicked in the teeth I tend to be quite neutral about it afterwards.
His overt claim that Ukraine naturally belongs to Russia I his war announcement speech and the premature, quickly deleted victory announcement from state media announcing that the victory in Ukraine was to be follows by a new pan-Russian union between Belarus, Greater Russia (a historic term for Russia proper) and Lesser Russia (a historic term for Ukraine) suggest that “neutralized” is not the goal.
> They already succeeded temporarily once with the Warsaw Pact.
None of the Warsaw Pact members (especially not Ukraine, which was a republic of the USSR) were neutralized, or even merely friendly, they were Soviet-dominated states that would be invaded of they strayed from the Soviet line too far.
Yes, establishing the borders the metropolitan state had and the control of the peripheral states it exercises under the Warsaw Pact might be what Putin wants, but that goes far beyond “neutralized Ukraine” and threatens a number of current NATO members.
IIRC Romania is in NATO, Moldavia isn't. So invading Moldavia too would just, by eliminating a bit of border with a neutral country, give him an even longer border with NATO. Thus even more putting the lie to his alleged "Must avoid NATO countries on my border!" motivation.
OTOH, if Moldavia is already in, then AFAICR from its shape on the map the length of the Russia / NATO border would hardly change at all (because Moldavia's western and eastern borders are about equally long), so neither would the "calculus".
Why; is there anything wrong with it?
[P.S:] Oh, and it wasn't my "calculus" originally; it was @usrusr's. At least if I understood them correctly.