I don't really agree with this. I think HN gets a pretty decent mix of all political viewpoints, just based on the percentage of times I see stuff that I agree with (politically) and the times I don't. If anything, the thing I really like is the stuff that feels blatantly tribal one way or the other is still consistently downvoted. To your specific points:

1. "as its user base aged from young, hungry, hopeful entrepreneurs to jaded senior engineers or VPs in large fortune 500 companies" I think that's a vast, and honestly unfair, over-simplification. I think a lot of folks have become genuinely disillusioned, and it really has nothing to do with changing with age (heck, if anything, I see young people as being more disillusioned than I am). For example, not speaking so much of any political change, but I certainly vastly underestimated how effective the Internet and social media would be as a tool of division. And I personally have some regret of some jobs I had that made this situation worse.

2. As HN has become more popular I've seen a large influx of more right leaning viewpoints. Of course, I think that's probably just because I consider myself more left/centrist, so it's hard for me to say if there has been a real change in direction, but I think I have seen more just blatant political takes, but again I still see informative, quality comments still bubble to the top most frequently.