You raise a good question because it seems fitting to use weather in order to win any single match without having to play your way around the opponent's team with extreme difficulty. Spamming Water-type attacks, Hurricanes and Thunders is a perfect deal for striking as fast and hard as they come and getting the job done.
Sand may function in a way that racks up residual damage and slowly whithering down the opponent bit by bit, but the objective remains the same. Weather wars are in essense, a counter to the weather you're facing. As mentioned earlier, the metagame seems to be at a point where you're stretching the boundries of team building to ensure you come out victorious in the weather war.
Essentially you will find "pilot mode" amongst strong weather teams, where experienced players ladder in succession to whipe out enemy teams with a dominant strategy.
When you don't focus your team building on catering for the vast array of threats seen inside rain/sand/sun, you will find yourself losing as many games as you are winning. If you don't run Tyranitar/Gastrodon/Kingdra and you have rain opposition, immediate advantage is in favor for your opponent, as he/she won the hardest part of the battle already.
Would non weather be more viable assuming we look at various suspects banned already? I'm talking Excadrill, Garchomp and Thundurus.
-Excadrill allows you to set Stealth Rock on the field, Rapid Spin and thrive against sand teams: would this work on non weather? Hell, yes.
-Thundurus can incapacitate fast sweepers in rain, whom are incredibly strong under such weather, and he also sports amazing coverage and the ability to take advantage of opposing rain teams.
-Garchomp was a universal masterpiece as far as Dragons were considered (until we see Salamence and Dragonite additions come flying in), and granted you the option of building a solid team around Garchomp. "My rain team can't hack the opponent's sand offense; guess I better send in Garchomp to ruin their day!"
I think non-weather is viable, but there's only several players who I could trust to actually accomplish anything with non-weather whilst trying to keep up with the common trends today.
It just seems to me the sensible option is to dedicate two or three slots to gain instant advantage in opposing weather teams and allowing the remaining half of your team to revolve around a strategy which comes down to your own imagination.