They should release new level 50 Guildhests which are designed explicitly to teach mechanisms from EX Primals/Coil. I think that was the main point of Guildhests throughout the game, teaching key mechanics such as dealing with adds, prioritizing different targets, etc. Perhaps the update following a release would be an ideal time to release this, so it doesn't change anything for the first wave of Raiders who go in and work out strategies on their own. So when Coil 2 came out, something that had a fight with a mechanic like Divebombs or Twistsrs from T5 could have been released, to give people a way to learn without all the learning group drama and issues like above.

And SE would need to INCENTIVIZE running these for players who knew the content, perhaps with a daily roulette that awarded tomes and a possible minion or mount drop... NOT GC Seals or crafting mats. Adding an increased chance of mounts dropping to EX Primals is all well and good, but all it does is give experienced players a reason to repeat the content with each other.