I've been around long enough to see shaft drive overtake belt drive and now belt drive becoming the hot setup again.
Belt drive has more friction than shaft drive.
Take my old HPI Mini RS4 (belt drive) and Cup Racer (shaft drive) and roll them both on the floor. The Cup Racer has noticeably less drag.
Take my old Align TRex 450v2 (belt drive) and new TRex 450 Pro (shaft drive) and spin their rotors. The Pro has noticeably less drag.
Being an old guy, I've had the Kyosho Optima "Mid", the original Yokomo YZ-10 "Dogfighter", the HPI RS4 Pro3 and RS4 Mini. They all ran well but had drag. If the belt is exposed it has the nasty habit of picking up detritus regularly and needing clearing of the pulley. Plus the belts would wear out fairly quickly - especially the rear drive belts.
I've sat out the whole shaft drive generation of RC on-road cars waiting for the designs to "settle out" and then to support brushless motors and LiPos. Unfortunately for me the designs settled out with nitro track cars that can't run on the street and have no bottom-end and ugly bodies - not to mention the hassle, expense, noise and oil residue of nitro.
Since nitro track cars and the touring car standard have all but killed on-road racing, I've been looking for electric (hopefully) shaft drive on-road cars myself and have given up on finding cars that are designed for brushless motors and LiPos. At this point electric on-road cars are so hard to find that I'm happy to find anything that is interesting and affordable. FYI - The Associated TC5x-TC6x are too expensive, too tweaky and can't run in front of the house.
So here are the only two decent shaft drive electric on-road cars that I can find: the HPI Cup Racer and the Tamiya TB-03 series. Both of them are nice cars but are also old and I wonder how long parts will be available for them. Once these cars are gone what will replace them?