What Sean left out was -- overfunded for whom? He implied it, but didn't say it: the bigger dogs in the fight (Facebook/Twitter/Google) have to compete for talent like everyone else.
The overfunding is mostly a problem for those larger tech companies, not the little guys.
I suspect he means that investors are overvaluing small startups (relative to their chances of becoming successful). The consequence he worries about is that having too much funding available makes the opportunity too appealing to the best engineers, making it harder for ventures that will succeed to keep/attract talent.
His arguments seem a big reach, though. Lots of investment means opportunity recognition, and there are a finite number of engineers, so supply/demand takes it course.
He's arguing against capitalism, and not making a very good one at that. While trying to sell this as an industry-wide issue, I suspect his real concerns are more immediate -- for his own ventures.
He's not arguing against capitalism. He's saying that the market is currently overvaluing certain kinds of businesses, causing resources to be misallocated. That's it.
You may be right that he is either wrong or making his argument for self-serving reasons. Or he might be right.
The overfunding is mostly a problem for those larger tech companies, not the little guys.