No blizzard doesn't rely on raiders to carry the LFR crowd, That is why LFR is tuned the way it is.
Also your small percent of runs doesn't account for all. I have been in many that didn't have Heroic+ raiders and guess what...we finished it.
If raiders above LFR stopped going in there it would still be completed just fine and if it didn't blizzard would tune it so it would be.