I was considering the 30 min as brutto times. So 30 mins are 30 mins. The only thing to consider then are frequencies, if they are bad (which they are in most of the US admittedly).

Anyhow. This whole scenario sounds bemusing and absurd to my European ears. Do you only have one supermarket in town or why do you have to do a small world travel like that to get there? Is that what splendid car only urban planning turns cities into?

It all boils down to the fact that if you build cities primarily or exclusively for cars, transit sucks. It is like getting around in Venice by car. Of course it sucks (you are basically limited to drive in circles in the parking garage). I take neither car nor transit to make most groceries. I either do that at a transit exchange, on my way, spending practically zero travel time for it or walk 3 min to the store. I rarely feel the need to go to a hypermarket but if I do, it is a 5 min bus ride add a few min more for total travel time. That is only possible because my city is not primarily built for cars. Of course that's nothing that can be achieved over night. However consider that it took the US also many decades to bulldoze its cities for the car. After all, they used to be built for transit as well before.

PS: What might blow the minds of many US Americans is also the option to combine, simply having a nice walk, with going to the store. You know, a bit of relaxed physical activity, seeing the the hood and doing the chores all at once.