If it were that easy, everyone would be clearing mythic raids in retail. But, they’re not. I’d be wiling to bet that most people aren’t even clearing heroics as guilds; they’re probably stuck on LFR or raiding regular and progressing through heroic. Raid mechanics have become increasingly difficult. Anyone who’s progressed through any of WoW content has raiding experience. That does translate back to Classic. You can’t build coordination from watching a video or reading a strategy.
What you’re saying is the same as saying as guitar players are no better today than they were then because of the internet and various resources, and that PRACTICE has nothing to do with it.