Describing it as "convenient" does not make also make it any less true or accurate, which are the true metrics a framework should be evaluated by. We can't disregard frameworks just because we don't want one side to benefit, we must evaluate frameworks on whether they represent reality.

If Russia starts nuclear exchanges yes they will be solely responsible. They are being aggressor.

Also, they signaled wish to expand beyond Ukraine multiple times last year.

There's exactly one country threatening its nukes, conducting the largest war in Europe since WWII and showing no willingness to stop.

So, the question is: what do you do? Sit back and let it take whatever it wants?