True
But you act as if hes so limited as not really use at all
He did all those did Tsukuyomi twice and amaterasu once in the same day in part 1
Also in the final Sasuke fight in which he was pretty much blind he did each and every MS tech
Hes got a variety of powerful jutsu us that he can use, however, if any of them happen to fail against his opponent, then he would be in trouble. Susanoo, amaterasu, and tsukuyomi are heavy chakra drainers, and with someone of his stamina, he would likely run out before he defeated his opponent. When he used it against Sasuke, he was able to keep it up for a while, but in the end, he died due to chakra exhaustion, not because of his illness.
People tend to think that his illness severely hampered his chakra reserves, which It didn't. It was just slowly killing him, and he wanted to fight Sasuke before he died.