Frankly, the Mentor system needs more of an overhaul to help improve its quality. Currently, it assesses only a player's 'experience' (in a very crude fashion), with barely any regard paid to the quality of the player and their general demeanor. That's a problem, because for a Mentor, experience alone isn't sufficient.

I'd propose a larger revamp, one which absorbs the following two ideas:

(1) Mentors should come in tiers. Bronze, Silver, and Gold. There are plenty of players who would make fantastic mentors who don't grind some of the harder content (or, in the OP's case, Healer to 60). There should be Mentor tiers that account for that (with perhaps the Mentor icon being automatically turned off in instances to which it doesn't apply; for example, a Bronze-level mentor might not have their icon showing if they're in an Alexander Savage run).

(2) Mentors should be reviewed. Players in a party with a Mentor (or possibly only 'new players' having the designated status) should be able to quickly flag a Mentor with a negative or positive review at the end of a Duty Finder event. Too many negative reviews should revoke the status (temporarily), with a permanent revocation being allowed for repeated negative reviews. Mentor status cannot be something that, once obtained, no longer factors in to the mindset of the player.

In return for these changes, feel free to reward Mentors with other perks beyond a proprietary Roulette as needed. But they need to be evaluated, and they need to allow for players with significant (but not exhaustive) expertise to get a foot in the door somehow.