Yeah it makes a world of difference. I think the default is Hot but it becomes stale after a while. Currently I switch between Top 6 Hours and Top 12 Hours during the day, and it feels like I'm seeing everything new.
What client are you using? I've been using Liftoff and Jerboa for a bit here.
I'm using the dark theme. I like how it looks, but I think the UI needs improvement. When I tried old.lemmy I find found learning new things about the site that I hadn't seen before in the default layout.
Yeah I hope there comes more themes. Should not be difficult to install either for the instance admin. I think people just usually use the mobile apps so it's not something that is requested often.
Yeah there is something to be said for the fast and functional style. I don't know if you read Hacker News (https://news.ycombinator.com) but it has also stayed with it's traditional look through the years, when every other website embraced "modern" design. And their users love it.