LFR ruins the fight only in that you can see it. Which also happens with vids of heroic kills. But with the heroic vid, you actually see the whole fight instead of the nerfed LFR version.
BTW, there have always been bad raiders who can't do the mechanics. Back in my day, we took them on some trial runs, saw that they were incompetent, then dropped them. It's even easier now because you can take them into a LFR, log it, see that they suck and have no clue about mechanics, and drop them. That way you don't even have to bring them into a real raid.