Everyone so far is missing a point of confusion on the part of the poster.
They seem to first be asking “what is the point of apps”, because “everything else you just use the browser”.
But they also ask about downloading directly from the publisher. So, I think a couple of different concepts are being conflated here.
I think you just aren’t looking hard enough. Lots of apps are useful, run on your Mac, and don’t have any back-end service or use the Internet at all. (A good example are Finder alternatives - I use PathFinder). And, indeed, CAN’T be implemented by a website. I guess you don’t have any need for them though.
As to whether to buy from the App Store or directly from the publisher that is your choice. The publisher will make more profit usually if you buy directly. And in some cases, apps downloaded from the publisher can have additional functionality that isn’t allowed in App Store apps. In the App Store column, apps there have had some vetting from Apple, have to meet certain standards, etc.
I think there is yet a third confusion here. Actually, I tried to search for an answer to how many apps are in the Mac App Store, and actuslly didn’t get any useful answers. But certainly there are at least thousands and probably much more than that. Maybe OP is expecting to find their favorite iOS apps also in the Mac App Store and is disappointed they do not exist.
Apple is actually encouraging developers to support all of iOS, iPadOS, tvOS and MacOS and has recently announced “universal apps”. Good luck with that! Great idea, but very difficult for developers. It’s a lot of work, and as well not every app “translates” well to the different environments.
will be lots of issues with touchpad vs mouse/keyboard. And the fact that Apple STILL doesn’t have a touchscreen laptop (like Microsoft Surface). When Apple should have been the FIRST company to implement that!