Somewhere in X-Plane there will be a lookup table to calculate each coefficient versus AOA for that aerofoil element. So ultimately X-Plane is lookup table based for aerofoils at least.
The airfoil designer decides the Coeffs vs AoA for each airfoil
section, not the sim.
Anyway, you are missing the point. Lets take an example;
Lets say you go for a 1 hour complete flight. Thats 3600 secs.
Lets say your simulation rate is atleast 30 frames/sec.
In other words, if you use a lookup table and want to hit book values
at all times, you will need 100.000 sets of data since WEIGHT changes constantly, also in cruise.
If you do the EXACT same flight, only with a small change in
Takeoff weight, you will need another 100.000 sets.
Now imagine if you do cross control maneuvres, stalls, engine cuts etc etc. you will need dusins of tables for each frame.
I can assure you that a 40kb .air file in MSFS is not capable handling this. A $15 million Boeing sim yes, maybe.. .
Cheers,
M