Yes the OEM Bullet is a clone of the Tomy Bit Char-g, and Yes the quality is not very good compared to the original Tomy Bit Char-gs.
One very obvious thing is the loud gear grinding noises made by the OEM bullets (and some other clones). This can be easily fixed with some lubrication (such as the grease that comes with Cybot!)
The steering problem isn’t just limited to the OEM Bullet or clones, I know of some original Tomy Bit Char-gs that have similar problems.
I am not sure what you have but the Bensu OEM Bullet (Blue Nissan Mini-GTR R34) that I have is exactly like the original Tomy Bit Char-gs. When I do my cleaning I take everything apart, the motor, the gear, the rear wheels and axel, the from wheels, the steering magnets, the lot…
The problem with the cars not travelling in a straight line all the time is to do with the torque generated by the motor as it drives one side (left rear) only, this causes the car to turn a little, the front wheels wobble and turn to suit this, as they are only held in a neural position by very fine finger springs.
The only major problem I find with the OEM Bullets is the front stabalizer swa-bar, this is of a very flimsy construction compared to the original Tomy Bit Char-gs as are constantly falling off. You may need to make you own, or fit an original.