How is Kenpachi "coming back stronger from death" different from what Ichigo deals with. It seems like its the same thing.
If it's the same thing as the description of his power in the
Spirits Are Forever With You light novel, then its actually not the same thing as that.
Kenpachi's power is, rather than to come back stronger after death, to match his power to his opponent's power. Unohana flat out said that Kenpachi, as a kid, was more powerful than her. But because he wants to have a good fight, he lowers his level to that of his opponent. Skill and circumstance then decides who wins the fight.
What Unohana is doing right now is attempting to force him to realize how powerful he is and get back to his true power level by forcing him to a near-death state, then fully healing him. Not because he gets power from being in that near-death state, but because he will unconsciously unblock the limiters he set on his own power little by little until he can utilize it fully.
Others in the thread have said this in summary, but that's the complete gist of it, I believe.