There is a lot more to a camera than a sensor. There is autofocus system, frame rate, physical controls, user interface, physical size, battery life, sealing, build quality, and a whole lot more.
You can not make a blanket statement like all FF cameras are better than all crop cameras because all FF sensors are better than all crop sensors. Other things come into play, particularly AF systems. Any in focus crop picture beats any out of focus FF picture..... we are dealing with systems that are balanced towards particular needs. There is no absolute winner for all situations..... there will always be cases where the unlikely candidate shines. Heck, an iPhone beats a 1DX as an inspection camera, but you don't see me disparaging the 1DX because of that.