On my last trip, I noticed that there seemed to be an awful lot of cabs cruising the streets in the area (Shimbashi) where I was staying, so I took a one-minute video of the intersection outside my hotel.

During that one-minute video. TWELVE cabs passed through the intersection.

There is always a line at major stations and hotels in Tokyo, and you should have no trouble finding a cab on any arterial street. They tend to cruise in flocks. I have never had to wait very long.

Granted, I've never tried to get a cab in Meguro in the rain at 8:30AM, but depending on an app when several empty cabs are likely to pass by your hotel in the time you're waiting seems like a waste.