Both big powers are trying to increase their influence on Ukraine but only one country instigated the violence and is trying to stop ensure Ukraine's neutrality by invading it. Yes geopolitics is shite and very dangerous but in this one case only one country decided the best way to influence is by violence.
FTFY. Hope it is not a Freudian slip. Also violence started since Maidan.
At least we can agree it has been a disaster for Ukraine.
You ask what Zelensky should have done after the invasion, perhaps there were two possibilities.
First, there can be a Zelensky the Honest. Having the disaster on his watch by picking the biggest bully as ally,
yet whom critically won't / can't let him "win", the Honest would admit to his people he should have followed neither bully gang, and they have died and displaced for naught. If he survives that, to stem the disaster, he would fly to Moscow to sue for peace with Minsk 2 as starting point. His bargaining power is considerable - he can help restore the lesser bully's relationship with Europe, which has many Eurbillion more reasons to agree than disagree; and the security of Europe, never mind US, was never capable of being threatened by the lesser bully in practice, let alone under imperial dominion. The biggest bully would be furious, but the Honest has actually helped them avoid another forever war, while doing them a huge strategic favour.
Alternatively, there can be a Zelensky the Hero. The war has been an unmitigated disaster, but the Hero rightly says the invasion was illegal, perhaps even unprovoked since he has every right to join any gang he likes. Hence it's a good vs evil fight, a presentation nevertheless best avoided while standing right next to the world's biggest and baddest bully. The fight is then cast as a matter of noblest principle, transcending all earthly pain and suffering, even if he knows he can never "win".
A NYT profile of him just before the war paints a showman used to and drawn to adulation, by collecting sycophants - but perhaps it is pure coincidence that adulation is exactly what big bully's gang is showering him, while helping him fight the lesser bully to the last Ukrainian.
Your choice? And which one is the real hero?