A clearance option would not divide the community. A clearance option would simply enable farm or weekly clear parties to group players who have already beaten the specific instance. This enables more likelihood in successful runs to be completed within the allowed time frame. Why should they disrupt their farm quick runs and turn it into a learning party for the one new dude that joined? Makes zero sense.
If a player that paid for their clear originally joined this farm party, however, it will become apparent based on their performance and they will just end up getting booted from the party and blacklisted. Obviously, there might also be the oddball with a previous clear who just isn't that good in the party. That person will get removed and replaced as well.
Your emphasis on wait times and taking whatever a farm or clear party can get also amazes me. You make it seem like PF farm or previous clear only parties have wait times that amount to years. It's true that they can take awhile to fill. I think most of the top players, however, can agree that waiting for quality players with previous clears to join greatly outweighs any new player sneaking in to join.
You're not doing the party or yourself a favor by joining a farm or previous win only party in the hopes of a ninja win. You're just asking to get booted and blacklisted after you waste the group's time wiping and making yourself look bad for leeching or trying to ninja a win lmao. The more you do this, the more your server reputation will go down too, resulting in end-game players not wanting you to join their party.
Even if they don't add a clearance option, it does not mean the current state will change. Veteran players have zero incentive to help new players. New players need to put in the actual effort to be proactive and take the initiative to learn the difficult instances. Make friends, join new LS or FCs devoted to the new player community. It's seriously not hard. That's how veteran players got where they are today - by learning and making the effort to clear content.