Decentralization is a principle that needs constant reinforcement against the forces of convenience and convention. I fully expect users to centralize on a few web apps that don't burden the user with managing keys or browser extensions.

The relay situation is showing signs as you point out. Most clients use fewer relays and they aren't selected to maximize decentralization (ideally they'd be random with care taken to achieve overlap with max # of users). Amethyst should be applauded for its 19 default relays.

I suppose that from here it's just good to keep in mind that decentralization needs reinforcement so if you see a howto that doesn't touch on it, a nudge and sats to the author to fix it might be cool.