I encourage you to actually engage with the material you are wielding as "evidence" and the material you are responding to.
From the conclusion of Putin's speech:
> Russia is open to dialogue with Ukraine and ready to discuss the most complex issues. But it is important for us to understand that our partner is defending its national interests but not serving someone else's, and is not a tool in someone else's hands to fight against us. We respect the Ukrainian language and traditions. We respect Ukrainians' desire to see their country free, safe and prosperous. I am confident that true sovereignty of Ukraine is possible only in partnership with Russia.
This is supposed to be evidence that Putin's goal was to conquer all of Ukraine? I will charitably assume you already know what "partnership" means in IR jargon.
Where is your evidence?
Regarding your other questions, Mearsheimer addresses them in his talk, which you apparently haven't listened to. There is a lot of historical context you aren't aware of.
> Your other arguments are literally Russian talking points to justify the invasion so I can hardly accept them in good faith.
This is your own problem. If Putin says the sky is blue, is the sky therefore not blue? This is anti-intellectualism par excellence.
I am not saying these things because Putin may agree with them, but because they are based in evidence and common sense. Know the difference!