My only issue was that you stated this with absolute confidence, so I was assuming you would have something beyond your own analysis to be that confident.
However it's a plausible theory, I am not saying otherwise and I can't disprove it beyond pointing out that no one has openly said it. It will take me some time to research Lloyd Austin but they seem very credible so I'll try and find the time to see what their opinions are.
If I was to try and change your mind I'd point out that what you seem to be suggesting looks like a really bad strategy long term. If your opinion is that the US is pulling a Star Wars V.2 and under supplying Ukraine to maximise damage to Russia then even if we assume that Ukraine has infinite access to weapons and tech it has a very finite supply of men, it cannot fight indefinitely and any territorial gains made by Russia are unacceptable to broader US foreign policy positions, namely the "rules based order".
The Russia Ukraine conflict is important because we can't have Russia set the precedent that Nuclear Powers can just annex shit, Russia MUST lose this conflict, or we will see a global race for Nuclear armament.
This conflict isn't in a place where the US can just put it hands on the scales and roll Russia over once it thinks Russia has suffered enough, so I disagree with the premise of your analysis.
What I find more plausible is that The West isn't doing enough, quick enough is because The West is in a place where it would rather do anything other than throw money into a war with Russia. Globalisation is collapsing, European economies are stuttering and Populism is gaining momentum. It isn't an easy political landscape for governments to throw billions at anything, nevermind a foreign policy issue. Biden is posting 5% quarterly growth figures and he might still lose in 2024, this isn't a good environment for governments to go balls deep in Ukraine.
That's my 2 cents anyway, sorry that's it's not particularly sexy.
/Edit: Forgot to insert my position on Putin's long term strat and again I'm very boring and think that he's hoping the truly massive amount of elections around the EU and most importantly the US brings more sympathetic leaders into play. His biggest win condition is a Trump win and US pull out. Smaller gains would be EU right wing Populists gaining power and pulling support.