I was driving bicycle for ~10 years and most weather. Scooter would be upgrade.
> How do you deal with being stuck in the 5pm traffic under 90F sun?
You wouldn't if you removed 3/4 of cars and replace them with scooters
> How do you ride it when you're a bit unwell (flu, cold)?
You take a bus. Do you also drive car if you feel terrible ? It's not very safe....
>What do you do with your helmet, boots and protective gear when you go to a restaurant?
I'd imagine if that much traffic moved to scooters the city businesses would accommodate. At least for helmet they often just fit under scooter's seat.