I would not recommend it on the Kanagawa side either (I actually think the Tokyo side is better than the Kanagawa side, at least inside Kampachi, because it's slower).
I used to live in Aoba-ku and it was my usual route for driving to Tokyo by car.
There are many flyovers on R246 where bicycles are banned, forcing you to use time-consuming detours unless you want to break the law. If there's no traffic jam, vehicles may move at 60 km/h and faster and believe me, they would not expect bicycles there, though I did occasionally see some brave road cyclists. It's an unpleasant road even in a motor vehicle, let alone a bicycle. I would take almost any kind of detour by bicycle to avoid 246 in Kanagawa.
I ride R246 from Kawasaki side to the Imperial Palace, on my commute. I kinda like it. It's a dual carriageway so there are no cars coming at me. Yes, there are a lot of lights in central Tokyo (63 in 20 km). That's just how it is. And it's not flat.
For flat endurance rides without interruptions, the best thing is a major river like the Arakawa. You can get through without changing trains from Chuo-rinkan to Horikiri.