All these radio use commercial chips in the front end of their receivers, and there are only two or three used over all the different brands.
Remote receivers allow the modeler to place the antenna in an orthogonal orientation with gives a better chance of receiving the signal. More important to the more aggressive flier.
The RF power from 2.4G systems is very low compared to the 72 MHz systems. But link equations to determine range depend on many factors other than just frequency or power.