Thanks these valid concerns. We would certainly like to improve the discover functionality in GitLab. Right now https://gitlab.com/explore is pretty limited. But the community is actively working on this. This month we introduced a commit calendar and I'm sure that it will improve further over the coming months.
On GitLab, if I stumble upon any repo I can't figure which language it uses. On GitHub it is very clear. It even shows percentage of programming language used.
Open Source helps in so much for learning about programming for a noob like me and GitLab no way does that as like GitHub. Thats the one reason I don't use GitLab much, though I have an account. And one more reason why GitHub shines over GitLab for open source projects.