10 years ago Spektrum didn't even exist. Today it is probably the top selling brand in the 2.4 market.
For the longest time it was Spektrum for the entry level to mid range stuff and JR for the high end. But Spektrum stepped on JR's spance with the DX8, DX10 and DX18. JR has now come out with a line of radios that abandon Spektrum's RF system.
It will be interesting to see if we start to see JR moving back into the entry level stuff to capture the newer pilots. Once a pilot gets set with a given 2.4 protocol it gets harder to move them to another RF system. That is how Spektrum did it.