I get 'do one thing, and do it well', but there's absolutely nothing stopping the i3 folks from putting sensible defaults in the config for controlling brightness, sound, etc. It's simply a lack of care for the user experience.

I have tried regolith, but I found it to have weird conflicts between i3 and gnome. It may be worth another look though.

I'm not sure what kind of defaults you would like to see. For instance I have this in my i3 config:

bindsym XF86AudioRaiseVolume exec --no-startup-id amixer sset 'Master' 2%+ bindsym XF86AudioLowerVolume exec --no-startup-id amixer sset 'Master' 2%-

but there's no guarantee that this would work everywhere depending on what's installed, I just know that it works in my case. It's easy enough to look up anyway ('linux change volume from terminal'), so users would just save 5 minutes if the default worked for them. I think the message is that i3 is not targeting the same people as Gnome, and it's fine. Different software for different needs and trade-offs.

MATE with i3 as its window manager is excellent. No compromises, neither gets in the other's way. I wrote how to set it up here: https://www.mattgreer.org/articles/mate-and-i3/

This. I just install debian with MATE, install i3 on top, clone i3 config file from my git repo and all setup is done. Sound works, brightness works, external displays work.

If you're at all interested in tiling window managers, I can't recommend regolith enough. It's built on top a minimal ubuntu install and gnome-settings-daemon, so it gives you most of the non-window manager desktop stuff you would expect. At first, the distro was all the same stuff I would uninstall/install to roll my own environment. But they keep working on it and expanding the docs.

The only difficult part for me, is that they change the i3 config defaults. So often, instead of checking the i3 docs, I have to read my local config first.

I just wrote in another comment that I wish I had a little more desktop in my i3/sway, and this looks to be the ticket.