This factory amp is designed to make cheap factory speakers sound better. But it doesnt do you any favors when you replace the stereo or those stock speakers. Retaining the factory amp usually makes it easier to install a new stereo, and in some vehicles thats your only option.

Can a car radio work without an amp?

The truth, however, is that every single car audio system absolutely needs to have an amplifier. But the fact is that every single car audio system actually includes an amplifier, even if its just a weak built in amp, and your stereo literally wouldnt work without one.

Should bass be higher than treble?

Yes, treble should be higher than bass in an audio track. This will result in a balance in the audio track, and will additionally eliminate problems such as low-end rumble, mid-frequency muddiness, and vocal projection.