You're old-fashioned!!
In the beginning there were only 2WD cars. Then, along came a 4WD car. At first, they were mostly equal round a given track. As 4WD developed, and the Stock motor rule was abused, it became easier to distinguish the classes by the number of driven wheels.
It has always been possible to arrive at a track with any number of cars and pick the best one for the job. I used to run an RC10 with the MIP 4WD conversion. For 2WD I removed to the front suspension and gearbox and replaced it with the RC10 suspension. For 4WD, I put it back. When the classes ran together I chose which one was best for the track.
No, Cragg, Martin, et al do not turn up with a large range of cars because the they are sponsored by one manufacturer who would not allow them to use someone else's product in the same class.
As a matter of interest, what is the difference between a mid-motored 2WD car and a mid-motored 4WD car under people's definition of "a 2WD car is a 2WD car... etc.?" I am struggling to see how I would know one from the other!