I'm not offended that the OP generalized millennials. I get that he was trying to be humorous.
I work in a highly technical area. My company is huge, but I work in a smaller area and department with a lot of advanced degrees and strong personalities. If you're of particular usefulness, you generally become entrenched because you become too valuable to lose. There's not a well-defined technical track at my company, but there is a well-defined managerial track with many levels. Those who end up in managerial positions are often not technical powerhouses. Some are also insecure to the point where they prefer (and promote) underlings who go-along, make no waves, and won't argue with them.
In other words, I work in a place that's full of drama, insecurity, and BS. So I sympathize with the OP, and I understand that he came here to vent... and I'm here to provide that hug that he might need.
I've never understood the threat of "going to HR". I feel that adults (in most cases, including this one) should be able to work things out on their own. I mean, I understand that HR is needed in some cases, but I've been threatened more than a few times with the HR thing, and I've never seen it as a threat. I'd tell HR my side, and in most cases they saw it my way (or at least pretended that they did). From my perspective, HR mostly just wants problems to go away, and they do the least possible work to make it go away.
I suppose that I am fortunate; I made myself indispensable after less than 10 years at my workplace. If I have strong feelings about not wanting to work with someone, I have enough clout to eject that person from my work. It hardly comes up, though. I may not always be very nice about it, but I can accommodate most people... even the dumb ones. They are prevalent. Get used to it.