Your comment got me thinking... Is this a big deal, or even a small deal?
I think it's a deal of some proportion. If someone is trying out Linux for the first time and stumbles across how Flatpaks work and starts exploring Flathub, maybe their initial impression will be good enough to consider switching. If something appears to be polished, then maybe it is.
Perception is reality; while hardcore nerds are willing to roll their own distributions, there’s a reason Ubuntu is damn popular. Most normal people want their computers to work, and to have an easy discoverable ecosystem.
I've explained in another comment. They have these pages that seem arbitrarily made up to fulfill certain needs but not others.
You can get a list of packages sorted by popularity and with paging, but no filtering.
You can get a list of packages with filtering but it's limited to 1,000 packages for some reason, no pagination, and no sorting.
The way to find these lists is really unintuitive (go on, try to find the second one I mentioned).
There's no package count, unless you find the filter page and add up certain categories (I'm guessing they have about 2,600 packages but it's just a guess).
I have no idea why they can't just put everything I mentioned in one place. There's no reason they can't have a page with search, categories, sorting, pagination, and counts. I struggle to think why this one page can't be the homepage (with whatever defaults they think it makes most sense, like most popular packages first by default).
Having a homepage that only shows a handful of categories and a handful of apps in those categories really hurts discoverability. You'll never be able to find an app like Stellarium for example if you don't already know its name – and this applies to the vast majority of those 2,600 apps, and it will only get worse as they add more.
I'm guessing they made this design back when they had very few apps, took a lot of time to release it, and by the time they did it was already outdated.