1) Not everyone who doesnt has cleared a certain type of content, even WANTS or can (by can I mean: having the "personal" skill, as in being good enough by themself) clear that content - so the number that would actually be intresting is "How many people want to clear said content but havent yet?" (Judging by the amount of learn vs. farm parties I see in DF... there seem to be a lot more people who want to farm than those who want/need to clear)
2) Now that we have established that a good amount of clearless people might not even care for the clear, lets rethink "majority should be most important" - that sounds appealingly true at first, but is it? I say: Its not. Most often those people who are raiding/doing ex-primals are those who are really invested into the game, might have been for years and hopefully for SE will continue to stay loyal to the game. Giving reasons to farm those fights (for example the mounts - and even more so with HW now: Kill the primal 99 times, get the mount) almost screams "Farm me!" To keep this playerbase, who is actually intrested in that, happy by giving them the means to make farming easier (RF-clear-option) is a pretty good move by SE
3) You're focussed on the benefits of the newbies - but do they really benefit from getting paird up with impatient people who want a fast clear and will get upset at them because they're failing easy mechanics? No, they dont benefit from that. By seperating those people from those who are new (and those who are willing to teach/take it slower) the toxic behaviour in those fights gets reduced
Also to clear this up: Is your issue that less people are queueing for the content with RF (because you've got two queues) or is your issue that people who havent cleared it ar less likely to be lumped together with those who have?
Because if its the later it sounds a lot like "It is more difficult for newbies to get carried in DF" and not "Its more difficult for them to see the fight".
Expecting a carry and being upset when that doesnt happen anymore... phew...