Fights are all about control. Fights are even fought for control meaning either you and another man are at odds and each of you are going to beat the other man into a compromise and one of you will have control or you are both fighting to control a property such as a UFC title.
It's all about control. So if it's all about control why not pick the art that gives you the most control? A boxer has little control during a fight over his opponent. He is hoping that the opponent is willing to be in range for him to be attacked. If the opponent either backs up or steps forward then he is out of range and there is little the boxer can do to control his opponent and put him in range. A kickboxer is not much better. At first glance the correct answer would seem to be that a wrestler has the most control because he has skills that allow him to takedown opponents and be on top which is the most controlling position in a fight but the key word there is position. The truth is a wrestler who has no bjj experience might be able to control the position but the buy guy will end up controlling the fight with a fight ending submission and the wrestler will be willing to compromise so the buy guy will let him go.
The answer lies in a mix of wrestling and bjj while striking on the feet is at best minimally needed unless you are fighting in mma with time limits and judges that need to be impressed in case the fight goes to a decision.
If you want to be a great fighter develop both of those to the best of your ability. And throw in enough striking skills to hold your own and impress the judges, or set up easier takedowns. But the real control and the skill that counts in becoming the best is the grappling.