If I recall correctly, the requirements were purposely set so low to account for cultural differences between Eastern and Western playerbases. While most Japanese players enjoy leveling everything, it is less common among Western players, so the requirements were set low in order to ensure that enough people would be able to achieve mentor status on the non-JP data centers. Personally, I think such lax requirements were a disservice to the sprouts, as even if the requirements were stricter, there would still be plenty of mentors to go around.
Regardless, one thing I do think is necessary is updating the requirements as the game ages. Compare to roulettes: when new dungeons come out, we get locked out of DR:Expert or DR:70 until we complete the new duties. Likewise, the mentor system should require more from the mentors at each new expansion. Not necessarily right at expansion launch, but around the time the first raid is introduced, mentor status should be revoked from anyone who doesn't meet the new requirements.
For example, during the X.5 patch, an announcement should go out saying, "Beginning four weeks after the launch of Next Expansion Name, the requirements for mentor status will be as follows: [requirements here]. Any players who do not meet these requirements at that time will no longer have access to mentor status, mentor roulette, or novice network. Speak with a Smith after fulfilling the requirements to re-obtain mentor status." This would give players enough time at the end of an expansion to plan ahead so that they can keep their jobs current for the next one, and enough time at the start of the new expansion to carry out their plans to maintain mentor status without interfering with their enjoyment of the new content. At minimum, the current requirements should be increased to max level in each role and completion of the previous expansion -- I hope that much we can agree on. But even better would be one tank, one healer, one melee DD, one ranged DD.