This is right. The startup party scene largely acts as an echo-chamber. However, there are a few events out there that are designed around meeting people instead of pimping a particular company. Super Happy Dev House is a good example: It's mostly full of people that like building things but aren't brogrammers.

To find the quiet, experienced, skilled, well-adjusted people that aren't out drinking/partying once a week you have to actively seek them out while working. If you meet anyone like this, stay in touch. They are, by definition, not out there at events.

"introverted, seasoned professionals"

There's probably a fair amount of "introverted, seasoned professionals" that stop by HN from time to time. But then they reply with something that pisses the clique off, get down voted and never return.