I believe that grandparents point was that by not taking on any debt they don't have a credit score which can be verified. You can't verify something that doesn't exist in the first place.
I thought their complaint was that without a credit score, businesses don't see them as 'trustworthy'. The OP separated 'trust' from 'credit score', and says they shouldn't be conflated.
However since all of the OP's examples involved credit (car rental post-pay, phone usage post-pay, etc.) then in those cases trust===credit score. Without a credit score, you're basically asking someone to trust blindly that you'll pay back a debt since there's no track record of your ever paying back debts.
The problem is that I don't have an alternative method of proving my trustworthiness and as a result lose access to some products. Often times prepaid plans are not equivalent to postpaid plans, I can't just put a security deposit on a rental car to offset risk, etc.
