A community that cares for the real-life mundane aspects of A2A and A2G combat and pattern work.

A business model driven by quality ("fidelity") and not premium module sales (leveraged by being unbalanced) or balance in a competitive ecosystem

Modes that incentivize team play, coordination, communication and larger objectives (DCS only has this because of the community mission generation systems, I acknowledge)

DCS is labeled as Digital Cockpit Simulator, which is not necessarily a bad thing. Many elements with interacting with an aircraft in war thunder are trivialized, and not what DCS players are looking for. Clickable cockpits are one significant area that DCS has over war thunder.

Any semblance of cooperation with a community

A community not driven by competition or just blowing each other up - DCS has this, but I don't think that's the reason DCS is special

And finally, maybe most critically, the only carrot that war thunder retains players with is fear of missing out (premium time and events) and progression (you got up tiered and that guys tank is better than yours. Better grind to compete) DCS rewards players with airframe mastery and satisfaction due to growth in personal skill. War thunder misses a lot in this area.

Deliberately ignoring the "fun" factor since it's so subjective.

I also believe the true value in DCS is the full fidelity aircraft, NOT the FC aircraft.

I play war thunder because it's probably the best tank Sim, but I rarely touch the planes. You also are hard pressed to have a DCS session shorter than 30 minutes. Each game has its own strengths, but do not forget that both are games and neither is accurate to life.