How is the flight model? Is it on par with DCS?

Headache warranted, garbage based on low cost/quality potentiometers and generic gamepad electronics.

Minimal buy today is Thrustmaster T.16000M or their FCS or TCA (Airbus look, with better ergonomics) variants ~$60/70
or the HOTAS package of T.16000M plus TWCS throttle ~$130.

Reason is that T.16000M is the most cheap joystic stick available with contactless sensor in X, Y axes (Melexis MLX 90333 Hall sensor used in Warthog and X-56).

Second recommended option is the recently announced Gladiator NXT (contactless sensor in X, Y and twist rudder axes) ~$120-150 .... if find one for buy.
Or the older brother Gladiator Mk.II that still available in X-Plane.org store, too with contacless sensor in X, Y and twist rudder axes.

I've only played the stock careers. Yes, the AI definitely needs more work but I'm still enjoying the single player mode. I'm mostly a ground-pounder anyway so I deal mostly with the enemy ground forces.

I'm no expert but I've bought many of the so called top sticks/throttles/pedals over the years (I have a high end Thrustmaster HOTAS Warthog PC BL - $800, for example). The one I actually like to use is the above noted Gladiator-Mk-II (got mine in the X-plane store -- $100 when purchased -- its noted in my signature). If I were buying today, I'd probably buy the newer model, as suggested above.

Supposedly, the design was influenced by a WW2 combat flight stick (hand part). Its not an exact copy.

Depending on the realism of your cockpit build, it may or may not be good for your purpose.

I'll second Wings Over Flanders Fields. Most immersive WWI sim out there. Best AI you'll find. Lots of flyable aircraft as well.
Not the prettiest graphics, but on the other hand it allows for much more aircraft in the late war periods. Also, there's no multiplayer.

They have a WW2 one, Wings Over the Reich. This currently only has a few aircraft and the Battle of Britain though.

Ground pounding is my vibe as well.