Here's my issue with putting the ATC and other stuff behind a paywall that you can't take into Multiplayer:
ED constantly says that "the majority of the playerbase is in Single Player." So if they are, why not allow these modules and maps to be bought by the server owner and then everyone on the server gets to use them? It's not like ED will lose much business, and on the contrary, it'll act like an advertisement. You get on a server with it, you see how cool it is, and then you want it and go buy it later.
Also, I find it rather ironic that ED locks all these features behind the "everybody or nobody" mentality in Multiplayer. The Multiplayer scene is really all that's kept DCS alive over the years, because it's those server owners who put hundreds of hours into coding great scenarios and new scripts for the game that then make their way over to Single Player and enhance the game. Not to mention the regular stuff in Single Player is so god-awful that mission designers have to practically re-code everything to make it work as intended. AI with UFO flight models; Combined Arms that work sometimes, other times not; ATC that's three decades old and completely useless; the list goes on.
Multiplayer is honestly the only worthwhile experience anymore, so why continue to harm/fragment the community for the thought of a few extra rubles? Not to mention, Multiplayer isn't just getting on DDCS or Blue Flag, it's also those small personal servers that friends use to fly together. If my friend who only flies the A-10 wants to join my mission that I've set up where I'm flying the Hornet, why should he be forced to buy this DLC just so we can play together? It's just a really scummy business decision, and it screams disdain from the devs towards the community.