I've had mentors and have been a mentor, and yes, they are very valuable especially if they come to you (or you are available to them) at a time when it matters most. When you feel you or they are at the end of their rope.
Those that have mentored me, I have found their assistance and guidance invaluable, just as I have been told that my assistance and guidance has been invaluable. It's good to know you have people in your corner to keep you under their wing.
Sadly, society has devolved into a pool of "me me me all about me" and it's harder and harder to find a decent mentor, or to find someone to mentor.
I hope that trend doesn't last and the cycle breaks.
Mentors can alter lives. It's true.
I don't think that egoism is bad. But the problem the way I see it today, is people falling into a fantasy world. They have no tools to deal with the real world. Then what hapens is a big disparity between peoples skills and understanding and how the world actually works. They become like big children - narcisists who want "But I deserve this and that, others don't, buhuhu" the snowflake crybaby culture we are seeing that started with millennialls. Everyone want's to be successfull, but no one wants to do any god damn work.