I think if @Gargron wants people to adopt other instances, the onboarding process on joinmastodon.org needs a LOT more guidance beyond "here's a list of servers, good luck". Especially play up the shared-interest communities that instances can provide. Ask what people are into:
Make art? mastodon.art
Well-moderated community? awoo.space
Furry? Holy shit take your pick.
@timotimo Honestly, I don't think instances.social is that much more helpful for a layperson newcomer than the one on joinmastodon.org. You can't search by instance description for a community you might be interested in, and there's no way to filter out things like instances that are down or closed for registrations on the "Advanced" search page.