On the surface the Frsky Taranis and Flysky TH9X might seem similar as they both have 9 channels, but the short answer is the Taranis is a much better radio.
The taranis has better hardware, a better screen, voice telemetry, and better radio range/receivers. In addition you also have telemetry functions that some people even use as a lost plane finder based on RSSI. The Taranis also comes with a rechargeable battery and battery charger.
That said the TH9X is still a great R/C radio, and if you are prepared to mod it by installing new firmware, and also upgrade to FRsky TX it becomes even better. But as someone who owns both radios I would say that I definitely prefer the FRsky taranis X9D+ and do think its worth th extra money you pay. But that is just my own opinion