Of course technique and cardio are important. No one said to forget those and to just not train and go on a cycle and then become the 'ultimate fighter.'
Certain stacks can increase your cardio as well as recovery. The greater your recovery, the more frequently you can train at higher intensities. Increased training frequency leads to increased technique.
Let's not forget the inevitable odds of training injuries. On a long enough timeline it's not a matter of if they will happen but when. Certain stacks combined with intelligent rehabilitation methods will increase recovery allowing you to return to increased training frequency which will restore your cardio and technique quicker than not using.
I'm not trying to convince everyone interested in MMA/combat sports to juice, just to accept the facts.
If you don't want to use because of moral reasons, then more power to you. That is your individual choice.
The bottom line is that if you slack in training and then do a cycle expecting the gear to fill in for your lack of work ethic you will fail.
On the other hand, if you already have a strong athletic base and work ethic, supplementing with gear will make you all that much more of a monster.
Drug Tests exist for a reason. Of course just because someone pisses clean doesn't mean they didn't use, but that's a story for another time.