[isthisLOL?]

Well, you haven't really said anything but "he's popular, he MUST be good!". The artists you listed are far from incredible vocalists and all have major technique flaws that a vocal coach should get rid of within weeks with the exception of Gaga, who still uses flawed technique at times but only in really few songs because they require it. If he is really great, these are just uncoachable singers then.
Utada can't stay on pitch(the least fixable of the problems, pitch is by far the hardest of the "technical" aspects of singing), Christina has no control and no proper support, Mika has similar problems...and they all sing out of their range. He may be going for an ideal with his coached singers, he does NOT go for correct/healthy technique apparently.
(Of course there is always the possiblity that the coached singers simply do not want to use healthy technique since it will sound differently, I believe that's the case for Christina)