All of it tbh. Think about it, if NATO tactics are as inappropriate as you're making them why did they even train with them? Seems like a pretty basic thing to consider.

They're just plain old losing because they're a much weaker force than Russia. The actual truth is Russia's army isn't nearly as weak or as disorganized as western media pretends they are, it's actually a pretty large and modern professional army. Ukraine's army probably had good professional soldiers in the beginning but not nearly as much as Russia, and now most of them are gone. Recruits with a few months of training aren't going to win a fight against a bigger and better trained army.

Unless NATO steps in with actual boots on ground Ukraine is going to lose, there is no scenario where they win unless like you said there is a revolution in Russia, which again seems pretty unlikely no matter how much western media pretends Russia is unstable or whatever.

You're high on opinion articles from western media written by propagandists, not people knowledgeable in warfare.