Hertz and Avis shuttles, at least, are frequent, and usually fast. It'd be a slight positive to get Hertz Platinum style "driver drives to curb with you car, gets out, you get in, and the delivery driver takes a shuttle back to base", but I don't think I'd pay much of a premium for that. Maybe $25 per rental, tops.

At airports with big on-site car vending machines, you're not going to generally be able to do that at any scale without being arrested, and you'll probably be inferior to my current experience of walking across to the car vending area gold stalls, going to the number which was emailed to me, picking up my car, and driving off.

It might be more of an issue at smaller airports with no onsite cars, or where at certain hours all the shuttles are infrequent.