I will probably have to change my name and go into hiding after this post. If you never see another post from me on ATop you can surmise that I was banned permanently. But, here goes:
I don't think that Adam's voice is particularly well suited for hard rock.I think he is effective singing with Queen because he has the range for the songs, and he eats up the stage. His showmanship is something very rare these days, but is the essence of Queen as rock opera.
The typical voice I hear in hard rock is very chesty. Gruff. And pretty much flat in terms of resonance. There is the basic note, but it lacks the sub-harmonics that add richness and depth. How to explain? When you sing something in the shower, your voice bounces off the smooth surfaces and creates a fuller, richer sound, almost an echo. When you sing the same phrase outside in the open, there is nothing to bounce off, and it sounds dull. The rock singer may be able to belt things out very loudly and with power, but, usually without ring.
Adam's voice has all kinds of resonance and sub-harmonics. It's like he is always singing in the shower, even without a mic. The notes bounce around his body, his chest cavity and his head cavities. He has this "ping" or ring to his voice. Even though he can sing with great power on those belted high notes, through much of his range, his voice has a light, almost lilting quality. He can darken it up some, he can add grit, but it's still a light tenor voice. When he really powers it up, he magnifies the resonance even more, and he also uses techniques to sharpen the consonants and vowels in the words to give it bite. It gives the illusion of a rock vocal, but, sound frequency wise, it's not.
Adam's voice "fits" better for musical theater, arts songs, and light opera. (Come To Me, Bend to Me, and My Conviction style). There his type of voice is rare and coveted. However, Adam does not want to sing light opera. He wants to sing rock and pop. And, he does it very well, despite not having a voice made to fit that genre. He MAKES his voice fit the genre.
Could he actually sing like the typical rocker dude? Possibly. If he had never had classical vocal training, probably to an extent -- if he was singing incorrectly for his body and voice physiology. It would damage his voice over time, like that type of singing without classical technique has damaged other great rock voices. But, I don't think Adam will willingly abandon his technique and training and sing in a style that is harmful on the vocal cords. Even if he wants to be a rock god. The instrument he has is too precious to risk. And, singing with that resonance and ring in your body FEELS so good, from head to.... well, you have seen evidence of where it feels REALLY good.
I love the SHOW he puts on with Queen. It is such a total performance. It looks effortless, but, it is very hard work. I have fingers and toes crossed he will perform with them in the US, somewhere relatively close to me.
All this is just my opinion based on what I know about the voice. YMMV.