I have several planes on my DX8 with Spectrum RX, and the only time I ever had a problem was due to a bad ESC. I have dozens of flights on my DX8 without any issues. Before that I used a DX6i, same thing, never had a problem. Can't generalize saying Spektrum products are all bad. There are problems with Futaba, Airtronics, JR, etc. too.
For the most part these problems turn out to be user created due to lack of knowledge in setting the RX up correctly, or not using the correct connections, or servos.
Case in point, I thought my Futaba RX had gone bad when the servos were glitching and not responding, and the TX link LED kept blinking. Turned out to be a loose battery connection, even though I had a clip on the connector, the vibrations from the motor was causing it to break connection. I was about ready to rip the RX out and put another one in when I found the problem. One of the pins wasn't fully seated in the plug. It was that simple.