Is revenue really the defining factor of success for "open source"? Is higher revenue the indicator of "well funded"?

I think not. Open Source success would be indicated by adoption. And "well funded" indicated by sustainability of the project.

And in thos regards, Vue is both very popular and well funded. And among open source projects of current era, it is one of the most well known one akin to linux and git.

PS: Comparing a 6yr old project with 22yr old one is hardly fair. Not to mention that linux is quite big in scope