Overall, I think that the OSR has done a good job of bringing back a simpler style of rules for simpler types of adventures. I'm not sure that the stuff that WotC is selling is bad, only different. I know that when I watch players at my local game store playing in the AL adventures they seem to be having fun.
The other things the big books-in-a-campaign offer is a shared experience. Everyone who has gone through Out of the Abyss can share and compare their experiences with other gamers, whether it's IRL, or on Youtube channels, blogs, etc. Those shared experiences have always been an important part of the ecology of the D&D hobby.
And it should be noted that the WotC campaign books are way less scripted and railroaded than Paizo's adventure paths. So kudos to WotC for at least trying to encourage a setting-based, more sandboxy approach to play within their published campaigns.
There are an absolute TON of adventures available for play ranging from free to expensive covering the entire gamut of quality. Why would WotC want to publish these little modules with all their overhead and expensive writers when they can take a cut from DM's Guild community members writing decent stuff and cross promoting them in Dragon+.
In my personal opinion this is the absolute golden age of D&D content.
The thing WotC isn't providing is support for DMs who run their own settings and campaign worlds. The DMG includes a lot of good advice on creating a world and running your own homebrew campaign. But since they published the DMG, they've provided nothing. And I'm not talking about shorter adventure modules, which as you point out, 3rd party publishers have covered. I'm talking about DM aids. Lairs, NPCs, organizations, inns, ships, caravans, mercenary groups, bandit gangs, wizard guilds, maps of ruins, support for exploring forests, deserts, or underwater. Stuff that inspires and takes the load off a DM running his own campaign. Because at this point, a DM has the choice of A) running an entire campaign in a book, or B) making up everything himself. I think a lot of DMs want something in the middle.