Deere and Kubota only really compete at the smaller/utility side of things.
Also the reason people get locked into Deere isn't just the tractors, but the vertical integration. Can you run your John Deere NT or DB series planter with Greenstar 2 on a Kubota? Possibly, but you've got to buy the hardware from Deere and you'd have to add auto steer, etc. (FWIW Kubota doesn't even sell planters)