On demand is bad but not for that reason. people have places to be and are bad at planning. You should be running every 5 minutes so even if they are running late it still isn't very long until you get there.

every 10-15 minutes is cheaper and so because of cost you are often forced to be this bad (or worse) just to be affordable, but it isn't what anyone wants and people who use such systems will dream of ways to make a car work where they are

I live in a place where transit is about every 10-15 minutes and I never dream of a car. I mostly thank god every day I don't have to rely on one.