As far as Putin's "stated intentions", only the most abject of fools will take the statements of politicians at face value (and the fact that Putin's actions are not contrary to his stated intentions can in no way be taken to mean that his actions are not also motivated by other unstated intentions that are almost certainly of more importance to him than his stated ones).
And Putin himself is an abject fool if he is not motivated in some significant degree to counter the potential for further NATO expansion ... (hint: Putin is not an abject fool ...)
Of course there is something that could hold back western Ukraine from joining NATO - namely, the amply demonstrated fact that Putin's Russia is able and willing to invade Ukraine. Whether the West will choose to heed that very clear warning is another matter, of course, but to suggest that it would be a wholly ineffective factor of no significance is absurd.
As for Putin having so far shown no interest in installing a puppet in Kiev, see my remarks above concerning unstated intentions. Given the opportunity to do so - which he may well end up having - why wouldn't he? He'd be a fool not to - and whatever else he may be, Putin is no fool. An explicit guarantee of a non-NATO Ukraine may be the price the West has to pay to keep Kiev off of Russia's puppet strings. That Putin might not want Ukraine doesn't mean he won't use it as a bargaining chip to secure what he does want. A "double buffer" of a non-NATO Ukraine and a Donbass puppet is very much a real possibility, and one that Putin (from Russia's perspective) would be incredibly unwise not to seek and secure, if he is able to do so.