That's very poor understanding of what he did. What he said was we won't accept any more loans that we can't pay back and requested a sort of new deal for Greece which of course, included a large debt haircut.
He was never pro-Grexit. He was arguing that even throwing Greece out of the common currency was impossible, etc.
I understand that his way of doing things might confuse some people, but if you take the time to read/watch his interview his thinking is crystal clear: He wants to change the EU from within not disintegrate it. In fact he is trying to save the EU from itself (e.g. Brussels) by democratising the processes (e.g. add mics and records to Eurogrops, etc.).
Plus, I the ECB effectively closed the GR banks he had a plan of putting the ECB (Mario Draghi) against the Bundesbank. His own party kept him down stripping on of his only weapon by re-assuring the ECB behind his back that they'll not allowing him to use it. His plan was very clever.
And here is, I think, the problem. In general people don't take the time, and that's OK, but then they have not problem in having a strong opinion, that they read in some interested media.
My advice to the people so inclined is: check some of Varoufakis (and others) youtube interviews. Read a little about what is going on.
Check, for instance, how Spain was allowed to spend without consequences above the deficit limits just before the elections.
Check how, in the same way there is a limit to deficits in the treaties, there is a limit in surplus that Germany don't feel it has to respect.
Or just think how it's impossible that everybody is in surplus at the same time.
Or how all integrated monetary areas have deficit and surplus regions and that is OK because they have some way to compensate the unbalances.
For example if you read the picture The Economist paints around him, as opposed to Dijsselbloem (Dutch Minister of Finance) who is technically several orders of magnitude inferior is astonishing.
Varoufakis said that when he went to the US, at the beginning of his tenure, someone (Larry Summers?) told him that he'll be the victim of an organised campaign of character assassination by Brussels. I found this claim a tiny bit far-fetched, but on the other hand, the amount of false claims the established media kept throwing at him is amazing.
I came across ppl who thought Varoufakis as a buffoon like Trump, Boris Johnson, etc. and other political figures who can't put two words together. V is not like that at all, he is a intellectual beast, with a surprising ability to simplify rather complex ideas.
He had a plan (allegedly it was a Plan B) for the exit of the Euro if Brussels (actually Berlin) continue with the craziness. The Greek primer minister decided not to continue with the plan and he resigned as finance minister.
The primer minister could be accused of cowardice, but we have to understand that Greece was threaded with the shut down of its financial system in what, in the opinion of a lot of people, was an illegal movement by the ECB (1). It was a really difficult decision.
That's sort of my problem with him though. I don't think of him as either a hero, or a jerk, or a guy doing his job, but simply an idiot. He was trying to bluff with a hand that everyone knew was empty, and of course it didn't work.
Stathis Kouvelakis, a member of Syriza's Left Platform faction that later split from the party, had this criticism [1] about both Varoufakis and his successor Tsakalotos (another economics professor), which I think has some truth to it:
Tsakalotos said he was very disappointed by the low level of the discussion. In the interview to the New Statesman, Varoufakis says very similar things about his own experience, although his style is clearly more confrontational than Tsakalotos's. From this it is quite clear that these people were expecting the confrontation with the EU to happen along the lines of an academic conference when you go with a nice paper and you expect a kind of nice counter-paper to be presented. I think this is telling about what the Left is about today. The Left is filled with lots of people who are well-meaning, but who are totally impotent on the field of real politics.
[1] https://www.jacobinmag.com/2015/07/tsipras-varoufakis-kouvel...
This is telling about what the Euroarea is about today.
I suppose, at least it's a good thing if those naive professors, now that they are not so naive, explain the rest of citizens how the system really works.
At least he tried, for sure.