At first, I also thought that this was a glitch/OP/Broken, but then I think that this may be actually intentional.(Only the 7 tails needs to be fixed cause of combos glitch)
Think about the requirements for them to be used and the the requirements for other people.
Instant awakening: Available immediately. Can be gone in and out of almost instantly to gain the advantage over most people early on in matches. Cons are that either the persons chakra guage or health is depleted the longer the person uses it.
Adversity awakening: Availabe after the person's health is depleted beyond a certain point. Cannot be toggled on or off, but allows the user to stay in awakening mode for longer than anyone else and does not have any of the drawbacks like instant awakening. Usually good for the endgames.
Bijuu/Susanoo/other large awakenings: Only available after the person's health has depleted beyond a certain point (much farther than any adversity awakenings. about 1/4 hp left) stays awakened for maybe a minute.
The thing is, the power and invincibility makes up for the lack of ability to awaken earlier like the rest in order to gain the advantage if for a little while. Not only that, but their health has to be much lower, which puts them at a much greater risk for being taken out by people who can overwhelm them in their own awakening. It makes it much harder for the person to awakening and the person could have little subs by the time they awaken into their large awakenings. If that were the case, then they would still lose no matter if they awakened or not.
So they need a way to really turn the tides on their opponents, without really having to worry about their substitution since that might already be low and their opponent's subs and health are most likely higher anyways. Their large, high-powered, unfazable awakenings are meant to balance their vulnerability against those who can awaken much sooner than them and do more damage over a set period of time.
