I'm just going to come out and say it. Keyboard and mouse is garbage for playing games barring rts, fps, point and click adventure games. You used Dcs as an example and I don't play that but play flight simulator. It's significantly better to buy flight control panels, throttle quadrants, rudder pedals, flight yokes/sticks to play the game than to use a keyboard and mouse. It's also much easier to memorize the controls. Using a KB mouse combo for flight sim is also inferior to flying on a controller. Using the kb+mouse to control bank angle, pitch, and yaw is terrible. Horrible actually. As someone who has been playing flight sims since 98, I can attest from experience that it's terrible.
Personally, I don't know where this keyboard and mouse elitism stems from as its a pretty terrible way to play games barring fps, point and click, and rts. In fact, a strong argument can be made that point and click is better or touch enabled devices. Here are just some genres that are superior on controller: racing games, sports games, arcade flight games, third person shooters, platformers, open world games, etc. When I game on PC, I use a a controller for everything except rts and fps and sometimes, I even use a controller for fps games.
Finally most peopled do not want to memorize hundreds of button combos to play a game. 40 is already pushing it. When you have that many, it's no longer a game, it's a simulator and those make up a small minority of the market.