I don't remember any "intense diplomacy" other than more threats of sanctions, more public humiliation of Russia, no compromise on any question being discussed. In 8 years I remember Ukraine botching its obligations on Minsk agreements and Steinmeier formula.

With such strength of diplomacy, no wonder it didn't work.

What sort of compromise would you suggest? How much territory should Ukraine cede to Russia this year? And how much more next year when Russia manufacturers some new fake complaint?

Maybe none. Is "NATO" a territory of Ukraine? Is "no limiting of Russian language usage" a territory of Ukraine? How about "not overthrowing legitimately elected president, twice"?

So are you claiming that Russia should be allowed to veto internal Ukrainian political decisions, or prevent them from voluntarily joining other alliances? Wouldn't it be better to just keep killing Russian soldiers until they run out and retreat?

Well they are trying that now. It looks like the tide of war is not on their side at the moment.

And yeah, you should've got by now that the position of your neihbours is the most important factor in the policy of most, if not all, countries.