I'd definitely say there isn't enough RNG in combat and job design. People think they can make jobs more complex and engaging to play by simply adding more buttons but all your doing is just repeating the same pattern over and over, just slightly longer or an extra OGCD thrown in. Fewer abilities but adding various procs that determine what you should prioritize next would require players to pay more attention to maximize their DPS and solves button bloat issues. Red Mage and Dancer are the only jobs that kinda still follow this design but you don't lose much potency for failing.
Adding more RNG to bosses would make things less of a choreographed dance, but done within reason. Honestly, a lot of Normal fights have more RNG to them than Extreme and Savage fights because they're not designed with the 2-minute meta and maximum up-time in mind.