In AS, handling is based on “aircraft size” (an arbitrary, AS-specific category) and ATC on certified PAX/cargo capacity. Especially the latter doesn’t look very “realistic” and could/should probably be based on MTOW, indeed. The former is “fine” for the moment, but is something I’d likely look into once I start working on more dynamic airport NPCs or ground handling in general.
We already have two different pricing schemes in place. More recent game worlds have “formula-based” aircraft prices that factor in the actual performance characteristics of a given type. Older game worlds have manually defined prices…roughly based on real-world prices, but I am actually not sure about that 
. Either way, prices in both schemes can be adjusted if needed.