The difference is huge.

To take a bus from point A to point B, I have to walk to point C, wait for the bus, get on, wait to be dropped of at point D, cross the intersection to point E, wait for a transfer bus, get on, wait to be dropped off at point F, and finally walk to point B.

With this system I call a cab, wait for it at point A, get on, get dropped of at point B. Rather than my time being fragmented into 3 periods of walking interspersed with 4 periods of waiting, it is just 2 periods of waiting, which makes it much easier to make use of the time. In my experience riding buses, only about a third of the time spent is usable (except for long distance commuter routes), while nearly all the time spent in a cab is usable.

Even if the shared cab took a bit longer than a bus, I would still choose it over a bus for the improved productivity / enjoyment.

Lack of pre-defined and centrally-planned route.

That doesn't seem like a positive. People like predictability. They know their drive home takes X minutes, give or take Y, which is a small number. Having a different route every day makes the value of Y a lot more variable.

There's another aspect to "predictability." Back when I was a bus commuter, it was comforting to see the same faces every day. Even without chatting or acknowledging each other, there was a sort of familiarity to the strangers.

Is that a good thing, though? In practice the lack of a pre-planned schedule means that rideshare vehicles have to divert to get to you, being as much as 10-15 minutes away, which is not much better than just waiting for a bus.

Quickly catching a bus that isn't going where I want to go isn't ideal either.

It can pick you up at your house.