I disagree. Quality has certainly varied over the years, but HN is still miles above Reddit. I'm not a heavy Reddit user, but
every time someone or something links me to Reddit for something I might find interesting, the comments are mostly garbage. The same tired memes and jokes, over and over and over, tons of low-effort comments, not much substantial, curiosity-piquing discussion.
Sure, maybe there are some subs that are better, but I doubt I'd be convinced to spend more time on Reddit and less on HN. Certainly there are useful places on Reddit; I've gotten a lot of mileage out of searching for product reviews or general customer support questions on Reddit, but that's kinda a "single purpose" visit, not something for general curiosity.
I feel like there are some long-time HNers (your account was only created two years ago, but I'll give you the benefit of the doubt and assume you've changed accounts or have just been a super long time lurker) feel like quality has gone down; that's almost a meme of its own. Hell, the HN guidelines even has a blurb about how tired it is to suggest HN is turning into Reddit.
But I think it's a lot more accurate to say that quality ebbs and flows, and varies between articles and topics. And yes, sometimes the focus of the site (based on what submissions get voted to the front page, and what kind of discussion happens) shifts in ways that make my interest wane a bit, though always only temporarily. But that's not the same thing as quality.