No, it's different. WotC can't control who puts out a print book that is compatible with D&D, as long as it doesn't infringe on their IP. But they control who can sell their D&D compatible material on DDB.But hasn’t that always been the issue? At least for 5e?
3pp who put out some additional material for a WotC adventure path are going to be getting a huge leg up over another publisher who puts out a similar product but isn’t linked.
Which of course influences what gets produced and promoted. Being able to buy a book of add-on side adventures for Undermountain (as an example) that are already set up for Fantasy Grounds exist right now. How is this hugely different? Is it simply the issue of scale? WotC doing it directly is the problem?
The issue is that more and more players rely on DDB, particularly as it keeps adding features...such as selected 3PP. If you use it, you don't really want print books anymore, because they aren't part of the encounter builder, they don't work with maps, magic items aren't there to be added to digital character sheets, etc. Print material is just hugely inconvenient and undermines the whole point of having a digital platform.
So this already shrinks the market share available to 3PP, but by adding selected 3PP to DDB, WotC has a lot of power to create winners and losers.
Whether this is good or bad depends heavily on context. If you're a DDB user, it's great. You get even more choices and options. WotC obviously like it; they centralize control of the D&D brand, which is what they really care about, and can make some extra money on the side through licensing, though this is probably small potatoes. If you're a 3PP who gets to be on DDB, it's a fantastic opportunity; your stuff is right there in the DDB marketplace next to the official material, and completely integrated into the digital experience for millions of users (i.e. millions of potential customers). But if you're a 3PP who doesn't get on DDB, it's terrible, because as more and more people go to DDB, that's less and less people to buy your stuff.
SlyFlourish is also arguing that's it's just bad for the industry in general, in the long run, to have too much control in the hands of one company.