In summary, any time a whole series of new types of new options are offered there are a lot of ramifications to it (sometimes unintended) that do in fact offer a significant challenge to the idea that "The DM can always say no to a new option". Sometimes they cannot (AL or round-table DM previously approved), sometimes they didn't realize they shouldn't have allowed it in (future unintended interactions), and sometimes not allowing it means eliminated future publications from their game (because those future publications expand on and use the option they denied) which reduces the choices the DM has.
Just as quicker counter to your points here...
1) If you are DMing Adventurer's League or round-table DMing, you've gone into the job accepting that the game is not your own at that point. You have agreed to follow the campaign model of AL or the campaign model of a shared universe between DMs. Thus, I do not believe WotC needs to worry about catering their design work to those DM's specific needs. If a DM wants the ability to say 'no' to options, they probably should be running their own game and not one where they aren't in full control of what is allowed at the table.
2) I do not believe WotC needs to hold back on their design ideas because of the chance DMs make mistakes in their games. It's not WotC's job or responsibility to protect DMs from themselves. Especially considering that if a DM allows an option in their game and later on finds out it's not working... as I made in my original point, it's that particular DMs job as the the DM to fix issues that come up in their own game-- not relying to WotC to "baby-proof" the game for them.
3) It's also not WotC's responsibility to make sure everything they produce is to a specific DM's liking. Because that is impossible. They've *already* failed in that regard, because there's plenty of stuff in the core game that many DMs don't like and don't use. Are we to tell them they can't design anything further because they will inevitably be referencing rules in the core game that some DMs refuse to use, and thus that product is "useless" to said DM without a major overhaul? Of course we won't. And the reason being is that sometimes DMs
have to do some work themselves. That's part of the job of DMing. If a DM has a whole list of rules they have chosen to not use or have houseruled to run differently, and a future product references said rules... then the DM (if they want to use that product) has to do the work to change the product so that it fits their needs. And if a DM *doesn't* want to put in that work... then they should probably run their game as close to the default setting as possible to make sure that any future product could be run
without needing to adjust anything.
You can't make changes to the game at the start of a campaign so that it runs exactly the way you want, then expect any future product to conform to
that version you have put together. That's impossible. If you put in the work to make those changes at the start, that's great! Your campaign will probably run better for you that way! But you just have to accept you'll need to put in just as much time later on to adjust new things as well. It's what Dungeon Mastering is. It's work. Be prepared to do it.