This is something I've been thinking about on and off over the last couple months.
The conventional forum top page does give more information, but it comes at the cost of more clicking. The user needs to spend a bit more effort navigating around the site. And while the top page does usually include links to recently updated topics, it's usually only one topic per forum. So you have to navigate to see the rest.
The All Discussions view takes care of that problem by putting everything in one place. (Yes, I'm aware that other more conventional forums also have similar views. I'm talking about the fact that Flarum makes this the default view.) So in a sense, you don't really need the links in a tag-by-tag overview to keep you up to date.
The fact that the Tag page doesn't display statistics such as the number of posts in each tag is a different matter. There's a tradeoff here: while the Tags page lacks that info, it does a better job (in my opinion) of giving users (especially new and prospective members) an idea of what sort of topics are available in the site. It's more like a promotional tool than a user interface, if that makes any sense.
So I think it comes down to what you want to do with the site. Each approach offers its own set of advantages.
As for "intuitive", that question has more to do with the All Discussions page than the Tags page. Either is intuitive enough, in its own way; it's just a matter of becoming accustomed to a new way of doing things.
I'd also point out that the Tags page =/= Flarum. It's just an extension; so someone who likes the old way of doing things could conceivably replace it with an extension that works more like a conventional forum.
