Is there any reason to measure by percentage? If, before, we had 100k competent programmers and 0 incompetent ones; and now we have 100k competent programmers and 1mm incompetent ones—we still have enough competent programmers to get all the stuff done. Some companies will bother to wade through 10 bad hires to find a good one, and so end up producing a stream of excellent products, just as existed before; other companies (that wouldn't have existed before) will take the leftovers, and produce bad products that everyone ignores in favor of the good ones.
It's sort of like the fiction market: adding bad books to a bookstore or library, does not decrease the number of good books available.
I guess you could make the argument that if the low-quality products are well-marketed, they might outcompete the high-quality products—so, as a competent developer, the existence of incompetent developers (and thus the existence of companies who can subsist off their talents) might be "stealing revenue" from you/your company?
It adds friction all over the place. It's more difficult for a company to find the competent programmers, more difficult to find good books among the dreck, more difficult to judge which product is excellent and which isn't (without significant effort, in some cases). Rating systems can (and will be) abused, and finding the needle is harder when the haystack is larger.
Looking at hiring, a company might have to spend considerably more effort sorting through the "bad" programmers. There will be false positives+negatives in their search. How much damage will be done to the "good" products and the productivity of the "good" programmers because someone was misjudged when they were hired? How many skilled and passionate but less marketing-savvy programmers end up working for the quantity-over-quality companies?
If we had cheap, fast, and reliable ways to actually gauge the quality/skill of media/people/whatever, then more options would always be good, even if they're of widely-varying quality. As it is, we don't, so the extra options are something of a mixed blessing.
I can't speak directly for the programmer market, but this exact thing happened when steam opened the floodgates with greenlight. i used to browse the catalog to find new games; now there's so much crap in there that it isn't worth the time.
In my mind, that's just an argument for curation. There's no reason you can't let developers have their cake (i.e. have something up on Steam) while consumers eat it too (i.e. have a default view of Steam that hides all the crap games.)
I mean, direct-linking to things from a product site is still a thing; and—due to Steam technically being a website—discovery by search-engines indexing the page is still a thing. But also, there's no reason there can't be things like "App Store channels" where you can subscribe to a given app reviewer's "view of the world" (i.e. a store scope containing only the stuff they like, and—with less weight—the stuff the people they follow like, recursively); and then browse those, or a front-page that's the union of those. You could even automatically generate such channels from existing app-review sites/Youtube channels/whatever.
It's sort of like the fiction market: adding bad books to a bookstore or library, does not decrease the number of good books available.
I guess you could make the argument that if the low-quality products are well-marketed, they might outcompete the high-quality products—so, as a competent developer, the existence of incompetent developers (and thus the existence of companies who can subsist off their talents) might be "stealing revenue" from you/your company?