https://imgur.com/a/BfgJvWP

You have two main strengths from what I can see. Short fights the burst damage and ability to target switch without any downtime helps for speed running flashpoints and is also great in PvP as it can catch people out. Precision/ferocity + sweeping slash does a lot of AoE damage for cleaning up trash mobs.

Pretty much, and it's nothing about the way you play. You can be as dedicated as you like, but the games mechanics are stacked against you. You can line up one yellow damage heavy hitter during your precision+zen window, and it's fantastic in short fights, but no where near frequent enough to compete with other specs vs longer fights. Can you raid with combat/carnage? Sure you can, but today's player base is impatient and all glued to whatever numbers starparse is putting out. Any time there's a wipe they'll all blame you first "I don't think we have enough dps for this".

I've played carnage(combat) for a a while in 6.0 both low and high alac spec. Honestly it's okay for flashpoints but once you get bored and want to move on to raids you'll thank yourself for banking all the gold periodic intensity amps that you encounter along the way.