Being a Bosch owner myself, but I have ridden a Shimano powered bike for a few hundred miles. The Bosch Gen 4 non smart has loads of grunt and will power you over all manor of obstacles compared to the Shimano. The Shimano loves to be in high cadence and is suited to the fitter riders. It also seems to get better milage than the Bosch.
Problem wise, with our group it’s only the Bosch owners that have needed new motors! My old Gen 2 is on its 6th motor, but my Gen 4 has just clocked up 4k miles without any trouble but others have had them go at 2k.
Bosch have always replaced them with no issues.
Batteries will outlast your bike so don’t worry about them. At least the Bosch ones do. I’m still using my old 2016 batteries in my gen 4 bike as they fit into the frame.
Problem is with anything you get good and bad so it’s always a gamble.