Mythic rules, because they do so many things that go beyond ordinary applications of the rules, are always subject to a certain amount of GM discretion. If I were running the game and a champion spent one of their very valuable path abilities and a mythic feat to extend their throwing range, I'd say "heck yeah, you can throw that spear 200 feet." I could see a valid argument for the two abilities only adding a x6 range bonus in combination, but when it comes to mythic campaigns, I usually consider it best to err on the side of the more favorable interpretation. And either way, the range of thrown melee weapons should definitely be doubled by Mythic Distance Thrower.
(Side note: the real-life world record for the longest javelin throw is upwards of 300 feet. Considering Pathfinder's javelin has a range of 30 feet to the spear's 20, a 200-foot spear toss matches up pretty well with peak human performance -- and mythic heroes are far beyond ordinary human capabilities.)
Addendum: depending on lighting and environmental conditions, your champion might start having to make Perception checks to actually see their foes at longer distances.