I mean, the average user has been capable of installing and using alternative browsers for a significant period of time. Most folks exist as some shade of gray between your Grandma with an Ask toolbar and the "HN elites." If anything, I think there is often an underestimation of what regular users understand and are willing to do with their tech (to improve their experience, privacy, etc.) If you need some sort of a sanity check, see how your friends and peers (that don't work in software) configure their systems. See what browsers they use, what adblockers they configure, etc. I predict you'd be surprised.
I rarely meet this "average user" who is often discussed on HN; this person who isn't interested in using non-standard software, who doesn't care at all about their privacy, who will use only the easiest and cheapest solution possible, etc. Dark patterns don't just work on these "average users," they work on plenty who even work in tech. I click "Accept All" on the cookie banner on this one-off website if it's the fastest way to read the contents, I will put off changing default apps if I have to hunt for the correct settings, heck I've been charged for subscriptions an extra month because I put off dealing with the hassle of cancelling the thing.
I think this "average user" is constructed in the collective imagination because it makes implementing user-hostile design choices a little more conscionable if you view your users as tech illiterate morons. Considering the state of the industry, one where dark patterns and user hostility permeate nearly every design choice, it doesn't surprise me that HN, a subset of this industry, holds this dim view of its users.