Model Ys use something like 250-300 Wh per mile if you’re not at highway speeds, so I think your range estimates might be a bit pessimistic?

But yeah, I wouldn’t count on short grocery store stops to charge my car.

Thats... extremely pessimistic. I have a VW eGolf, with our 7.6kW home charger it can go from empty - full in 4 hours. It has a 36kWhr battery w/ a range of 150 miles, so in 30 minutes that's on average a little under 19 miles (probably more because you get faster charging at first and slower when closer to full).

But more to the point, how many people have a regular commute, only have street parking at home, and ALSO couldn't be expected to have their employer provide charging at work? Are they doing on-street parking at work as well?

I know a lot of folks in the city who own a car but use it for errands and trips but not commuting. They're the people best served by slower charging at grocery stores, movie theaters, etc. 20 miles isn't a lot but if you're topping up every-time you use the car anyways it adds up or at the least means you only need to use the fast charger once every few months at the most.