Raid finder was (probably) meant to help less populated servers by allowing them to queue to raids and ex trials with players from other servers (they were introduced before cross server PF), and it was kinda successful, many of my friends got their first clears via RF in midas and creator savage. I never got a first clear via RF but I've farmed a5s-a7s and a9s-a12s using it. The separation by early/late phase practice, aim to clear and farm (weekly clear) is imo necessary because of the difficulty (it's very unlikely that you can teach someone who's learning the first phase to be able to execute the whole fight in a single lockout of 90 minutes) and weekly loot restriction (completion queue makes sure all 8 people in the group have not cleared for that week).