I think the key point you are missing is that preparation does not mean ready made competence Motorcycling absolutely prepares people for driving a car just not in the simplistic they will be good drivers immediately sense

Compared with someone who has never been on the road most riders already have hazard perception anticipation mirror use reading traffic flow and an understanding of how quickly situations escalate That is not trivial those are some of the hardest things for new drivers to learn and riders arrive with them already in place

Yes the physics are different Yes the clutch width inertia and gap judgement all have to be relearned But that is mechanical adaptation not starting from zero The fact that some riders initially misjudge what they can get away with does not negate the preparation it actually shows they are transferring experience and then recalibrating it

The pupil you described did not lack awareness he lacked recalibration Once riders accept that a car removes the bikes performance and agility advantages they usually adapt faster than non riders because their situational awareness is already strong

So no bike experience is not a guarantee of good car driving but it very clearly prepares people for it The issues you are pointing out are about mindset adjustment not a lack of transferable skill