Putin is smart though. And this is where people keep fucking up foreign politics because they want to believe their rivals are stupid and don't know what's good for them. Russia doesn't have the same interests as we do and they don't even have the same interests we think they have. Only Russia knows what Russian interest are.
When you refer to another government as stupid, or crazy, or sociopathic you are basically shutting off any possibility of a diplomatic solution because you can't conduct diplomacy with someone who is irrational. Diplomacy didn't fail because Putin is irrational, it failed because western powers failed to understand some or all of Russia's interests.
I would not count Russia as a pariah state until they are cut off from Swift and other major economic isolation mechanisms. But as of right now dozens of European and western markets are poised to buy a shit ton of oil and gas from Russia this week.
Heres the thing about these limited economic sanctions.... They go away or become leasing meaningful over time. When you sanction, say, bank accounts to Russians sitting foreign minister, how effective is that sanction in 4 years when that dude retires and a new foreign minister replaces him? All the leverage it applied was lost. We know, and it is taught in security cooperation, that sanctions are less effective on Russia than say Iran or North Korea. Lots of reasons for that but they generally hit softer there. So in order to make an impact we need to ensure those sanctions are sharp and fast.
I wouldn't place the blame purely on Biden, I think Europe largely slept on this too, and in actuality I think the US made a good move to air blast the Ukraine troop build up for the last few months. This did two things. 1.) It removed any implications that the US or the west was going to be taken by surprise like what happened in Afghanistan. 2.) It placed the onus on Europe to rally effort to turn this. They have more trade tied in Russia than we do and more of a capability to make an effect than we do.
That said, Joe's diplomacy efforts were laughable at best. He wouldn't entertain what Russia said it's security interest were and instead wanted to entertain our security interest with offers like renegotiating the INF, something Russia really doesn't feel strongly about but we do. My diplomacy hopes were fully saddled in France and the UK but they were not able to close either.
Great comments by Macron recently though reminding Russia we have nuclear weapons as well.
All and all, whether or not this conflict was avoidable is hard to predict. The US Russian relationship took a massive hit during Obama's presidency. (Remember the disastrous Russian reset campaign? Or Obama publicly supporting Russia's colored revolution to overthrow Putin, something Putin was convinced the CIA was backing) I think of anything Trump came in with fresh ideas that were unconventional, and for the most part those ideas got headway. Biden's election though was a return to conventional foreign policy which could also be synonymous with Biden foreign policy. It wasn't working before so not sure why Biden thought it would work now.