I agree that people are doing it for the title and achievements, not for the purpose it was made for. Mentors have a bad reputation already among some players.

If you remove the achievement then what is the mentor reward? Not implementing that everything in game must have a reward.
But then not many players will be interested in becoming one.

I'd say make the achievements depend on the number of commendation you get as a mentor not the number of times you use the mentor roulette.
This will make people do their role as mentor properly in order to get commendations rather than seed run everything.