50 MP Medium Format vs. 50 MP Full-Frame: Any Difference in IQ?

Image Quality (IQ). It's what every photographer wants/needs. In that regard I was intrigued by the recent splash Hasselblad made by releasing news of its new compact, mirror-less 50 MP medium format digital camera, the X1D. For beginners like me, if you don't already know, medium format digital cameras have significantly larger sensors than so-called full-frame digital cameras. Correct me if I'm wrong, but the term full-frame refers to the frame size of 35mm film and is currently the largest digital sensor offering by many major camera manufactures such as Canon, Nikon, Sony, et. al.

So, I was wondering if the 50-megapixel medium format X1D by Hasselblad can/will deliver better image quality than the 50-megapixel Canon EOS 5DS / 5DS R (for example)and the comparable 42-megapixel Sony Alpha 7 RII, both of which have smaller full-frame sensors. (BTW, if anyone could provide the exact measurements of each senor format's length and width, I'd appreciate it for the sake of comparison.) Is there a limitation to the full-frame sensors that isn't apparent to me? Would the larger 50 MP medium format sensor be expected to deliver better image quality, or would the smaller 50 MP full-frame sensor deliver the same IQ?

To put it another way: would an image produced by a 50-megapixel sensor be expected to have the same quality no matter the size of the sensor itself that produced it? Is the size of the Hasselblad's X1D medium format sensor overkill? Can the same IQ be produced by smaller full-frame sensors with an equal number of pixels?

Inquiring minds want to know.