Demetrious Johnson, Dominic Cruz, Benson Henderson, GSP and Jon Jones are all wrestlers and dominant champions. Is it safe to say that wrestling is the # 1 fighting style on which to build a base as a true champion?
GSP doesn't really come from a pure wrestling background. He started with Karate, and then BJJ and wrestling, as well as boxing. If there is anyone that is a jack-of-all trades, I'd say it's GSP. He's trained in a lot of disciplines from a young age, not just wrestling like a Koscheck or Lesnar, or many other high school / collegiate wrestlers. I don't even think he did any amateur / pro wrestling -- just trained. Saying GSP comes from a wrestling background isn't really accurate to me. He just happens to be very skilled at it.
If you look at pure wrestlers who are stepping into the MMA game, many of them are in the middle of the pack (somebody said this already) - i.e. I think of Koscheck. Koscheck entered the sport as basically a wrestler with not much else. He's worked on his stand up over the years, but really relies on a heavy right hand more than movement, combinations, etc.
But to answer the question in the thread title, yes, wrestling is largely considered the dominant fighting style for a number of reasons. If you can secure a takedown you are controlling the fight (i.e. likely winning on points), probably not taking any significant damage, probably landing strikes of your own from the top -- and again, and most importantly -- controlling the fight in the judges eyes.
Worst comes to worst, if you are scoring the takedowns but not advancing position, landing good strikes or getting any submission attempts -- you can just lay and pray and still pretty much be guaranteed the win, based on points. Typically not a popular method of winning, but if you're outclassed in the stand-up it's a safe way to grind out a fight.