I think it's going to be pretty hard for you to argue that the proliferation of app stores for the PC is
bad for consumers.
A lot of people credit Steam (I think justifiably) with kickstarting a huge portion of the modern indie gaming scene -- precisely because they got rid of the crazy rules, agreements, and contracts of the retail boxes, which acted as a massive barrier to entry for game developers. If Steam had never been built, I don't think modern games would be even half as diverse or creative as they are.
Then we move on to storefronts like Humble and GoG, which I think have been hugely influential in pushing DRM-free games as the norm for indies. There are a lot of games that flat-out would not have DRM-free releases if GoG didn't exist. Heck, there are a lot of games that would not run on modern Windows if GoG didn't exist.
Then we move on to Epic's store, which I know gamers hate, but trust me when I say a lot of indie developers are thrilled right now to see someone forcing Steam to lower their splits. Epic has done some serious good for the indie scene. I don't like that they're encouraging exclusives, I think that's bad for gamers. But I'm not going to pretend that as a developer I'm not happy to see someone breaking Steam's stranglehold on the mainstream PC marketplace.
So yeah, there are a lot of PC stores. This has been a massive boon to the industry, there are a lot of excellent games that (I think) would not exist today if not for the diversity of marketplaces. And a lot of these marketplaces fill different niches. GoG focuses on older games, Steam offers mainstream AA titles, Uplay/Origin offer corporate AAA titles, Itch has all the really weird, creative "true-indy" stuff.
No single PC store is expansive enough to cover all of the niches of the entire market.
Even on the console side of things, the diversity of games on the PC has pushed console manufacturers to offer much wider selections of games. Are you happy that basically every indie developer and their dog is releasing their game for the Switch? A big part of that is Nintendo opening up the development process, and they did that because after the Wii U they realized that they needed to pull indie devs away from the PC to stay competitive.
And on PC, what's actually the problem with this? You can basically ignore all of the other platforms and just download your games from Steam. You can opt out of all of the complexity that you dislike.
Sure, you'll miss out on a few exclusives if you do. But you would have missed out on many of those exclusives with a unified storefront anyway, because a lot of those games just wouldn't have been created if there weren't stores that were a good fit for them to sell on. You'll miss out on just as many games if you decide to stick with curated console storefronts.