As far as the “flight model” is concerned, there is no one flight model in the sim… it’s all about the sim’s core aerodynamics engine and what it facilitates and how each aircraft’s flight model implementation takes advantage of it. Yes the default aircraft are nothing home to write about, but various 3rd party add-on aircraft have excellent flight models showing that MSFS is indeed capable of great flight dynamics. See this discussion for more details: MSFS flight models, aerodynamics, etc
Yes ground handling/physics is poor currently, but they’ve called that out as a focus area to start improving, and they already started in the SU10 beta to properly simulate tire ground friction that will alleviate the slipperiness seen on the ground: Any update to the ground physics/ friction model? - #7 by Europa279715
They have similarly said they plan to address proper water physics in the future.
Clouds are improving all the time and with the SU10 beta it is miles ahead of default or add-on weather in any other sim.