Now for theory purposes, supposed you could stay level at 90 degrees of bank, all that turning action would be from the elevator IMO.
How do you expect to stay level in a 90 degree bank? What exactly do you think is counteracting the force of gravity in this situation?
As a non-pilot, who's only experience of 'flying' is in air-combat computer games, I find the lack of basic understanding of physics displayed by some on this forum as frankly worrying. I'll probably get banned from the forum for this, but I'll say this anyway: aeroplanes exploit the laws of physics, they don't circumvent them. The only thing that keeps them in the air is the interaction with the atmosphere, and there aren't any magical attributes of aircraft that make them better at staying airborne than a dustbin-lid or a discarded lottery ticket. To be able to stay in the air, an aircraft needs to generate sufficient lift to balance its weight. To be able to manoeuvre, it needs excess 'lift'/thrust to change direction, and sufficient control response to apply this lift in the desired direction. End of story.
None of this would matter a damn to me were it not for qualified airline pilots apparently not understanding that one can recover from a stall by pushing forward on the control column/sidestick/whatever planes are controlled with now....