I wholeheartedly concur; gear only having cosmetic value would make WoW a much better game, in my opinion. The question is if it would remain a successful game.
I'm quite sure all these self-proclaimed "bleeding-edge mythic raiders", whose progress would purportedly suffer from the removal of LC would agree with you too, since "loot isn't a reward, but only a tool".
This does happen frequently, the 960-980 haste jewelry in my bags speak volumes. Which is why this change can only be implemented when item level upgrades become significant again. It's no coincidence that Blizzard's actually doing an effort to make this happen by changing efficacy values of primary and secondary stats.