then what makes you think that he will continue training as hard as he has in the past?
Because the Kyuubi's chakra is a ditch effort. Like a last resort. Kind of like what the 8 Tails talked about. Why would Killer Bee risk summoning him, if he had the upperhand to begin with. Killer Bee's answer was that he had not fought anyone as tough in a long time. When the odds pile on, that's why its time to use the Beast. Otherwise, its risky because the strain it places on the body. Killer Bee's skin flaked too.
But controlling the Kyuubi's chakra is not easy. Its extremely difficult. That's why he has to work hard. But at the same time, he has to train with his own natural ability, because relying on the Kyuubi soley could be life threatening. There's a time and place for everything. He has to work hard in order to Master "That Jutsu". Just because you are blessed with gifts, does not mean you can use them effectively without hard work. Sasuke being raped by Killer Bee is my primary example.
Sasuke should have used Amaterasu from the very beginning, yet he could not control it, and got raped. Not saying Sasuke should spam the Mangekyou Sharingan, but he was obviously getting grinded into dust when facing the tailed State Killer Bee. He should have used his more powerful techniques, but apparently he did not unlock them yet.