People still use flow-router and iron-router, but only if you still use Blaze as your front end.
These days I think most people use either React with react-router or Vue with vue-router. Since it became possible to use normal npm packages within Meteor (since Meteor 1.3 in 2016), many of the packages on atmosphere are no longer needed. Some packages on atmosphere are meteor specific, but because meteor is stable and updates are always backwards compatible, most of those packages still work just fine.
Meteor is very mature and very stable product - it’s rock solid and feature mature enough that it doesn’t need constant updates or fixes.
I would still recommend it for a long term project, and regularly start new projects with it all the time - because Meteor makes it so easy.
In my opinion, a battle-hardened, stable 7 year old product which is still receiving updates (Meteor) is a safer bet for a long-term project than the (relatively) new-kids-on-the block (next/nuxt).