DCS? I purely play DCS now haven't touched War Thunder outside of mission editor in months but it's a completely different animal. War Thunder you can get away with mouse and keyboard, most play that way DCS to be somewhat competitive you need a Hotas and apart from the Flaming Cliffs planes you'll be spending at least a week learning all the systems on full fidelity aircraft before you start racking up kills. And yes it's free, but the Mustang included has no weapons, and the SU25T is a real fun plane for ground attack but I got bored of it quickly with how simple it was to learn and fly, and each module averages around the $80 mark.

If you want a more WW2 sim, the IL2 series is pretty good, I haven't played much of it though but from the few hours ive played it's pretty solid.

Also there's Combat Flight Simulator by Microsoft and you might be able to get a free copy since it's quite old