I think the wrong premise people have is that a more expensive camera will produce better IQ. I would submit that a better camera, regardless of cost, will provide better IQ. Sometimes a lessor costing camera provides better IQ, and I think we all know more then a few instances of this.
But I speak of IQ here....And as to composition, what a better camera cannot do is make one compose better. Usually. And as to composition, every single 35mm camera made, every single DSLR ever made, regardless of make, of model, will never prevent one from composing a picture, so long as he has a lens with the required FOV, and aperture setting. But lenses aside, any and all cameras will not prevent one from composing their best work.
But, if one wants that composition to have the highest IQ, then well, the camera does in fact matter.
A resulting composition is the result of a conspiracy between the photographer and his kit. If the kit does not support the photographer's vision, then the resulting composition will suffer. Therefore, kit matters, and often it matters a great deal.
It's not becoming of a photographer to get "macho" on us with statements like "a great photographer can take any camera and produce a masterpiece". I don't believe this and never will.