Rarity

[Vidu]

You forget the real obstacle before starting the grind:
How to unlock Mentor-roulettes.

->One must have completed all dungeons / normal trials / 8-men-raids / 24 people-raids and all old Ex-trials (which is at the moment everything from ARR up to Stormblood) to have access to the roulette.

EDIT: Or, in short, you need to complete everything that isn't Savage-, Ultimate- or current Ex-content.

I kinda assumed that someone whos looking for things to keep them entertained that requirement wouldnt be to much of an obstacles, to be honest. Unlocking and clearing all of that content seemed like something one would do before looking for rare stuff to grind out - and even if OP doesnt have everything unlocked, they said they dont mind a grind. They did mention though that they usually restrict their characters to specific jobs/roles - something you cant do if you want mentor-status. So that might actually be the bigger problem here, before we even talk about the other conditions involved - like the 1.5 commendations and the 1k of completed duties or, in the end, the requirements to unlock the mentor-roulette.

[MelodyCrystel]

[...]Unlocking and clearing all of that content seemed like something one would do before looking for rare stuff to grind out - and even if OP doesnt have everything unlocked, they said they dont mind a grind. [...]

Not necessarily, when you consider people were already complaining in the past because some trials needed for Mentor-roulettes are locked behind sidequests. (Hildibrand's battles are a common example for fights players like to not complete.) Several optional dungeons are also falling into that category.

To add from my personal experience, I find the work one has to put into the Astrope-grind these days kind of overwhelming.
->Reflecting on all factors involved, I had it fairly easy when I picked the challenge up in the last winter of Heavensward a ka before Stormblood got released. Not as many recs needed to become a Mentor in first place; not as many completed instances to unlock the roulette; not as many troublesome trials possible to happen on the road.