From 1976 to 1983, Mr. Olympia was under 200 lbs. With the exception of 220 lb. Arnold in 1980. Wow, how times have changed. Then along came Haney at 240+ lbs, which pretty much ushered in the modern era of supersized bodybuilders.
I'd also have to go with Dickerson as being the least dominant Mr. O. But I wouldn't include Zane in that list because for three years in a row he was best in the world.