In a way, it can be used as a continuing education system - many people who really want to continue learning will have several mentors.
*MAJOR OPINION ALERT*
Ok, you have been warned.
Honestly, as mentors, we can't run other people's lives. I try the best I can with my students to help them with their reviews, but it would be impossible for me to teach each one everything about everything. We can only help with the reviews they submit to us during class, and once graduated their reviews are up to them. If they want continued help, many of us mentors let them know we'll be willing to help in the future, but it's up to the member to take advantage of that offer or not.
As for the question "Is it really enough to help them with 2 reviews and then send them on their way?" For a lot of people - no, it probably isn't "enough". They still may not be writing outstanding, EU reviews with no typos or errors. But what would be "enough" for everyone? And how would we measure "enough"? Perfect reviews every time? Is that even a reasonable expectation?
I know that a lot of us spend a lot of time and effort into mentoring students... but even so we can only do so much. Some mentors don't do much to help their students, and some students don't do much to really benefit from the help their mentors offer.
It's not a perfect system, and it never can be - because fallible people are involved in it. The mentor program as it stands now is still better than NO mentor program at all. (In my opinion, anyway.)
It helps new members learn the basic reviewing process, and then they have a foundation from which they can continue to learn - either by using other mentors, or by personally investigating things.
Also, when we see a less than perfect review, we have our vote with which to make a statement. If we see reviews, or posts on the forums with incorrect information in them - instead of blaming a mentor (who may or may not be responsible for said mistake) perhaps we could just take the initiative to nicely and kindly correct the mistake. The plus side of trying to be helpful is that we can get the Point Boosters on our accounts and earn more Eden Points for our normal actions around here.
To me, I prefer taking the attitude of "I'm here to help" rather than blaming mentors for not teaching a student absolutely everything we think they should know.
Your mileage may vary, and all that.