Doc seems more like the other ranger type, or a ranger type of ally, but who wonders about, similar to what I think the phantom ranger I read a bit about is like. & Doc would not remain in 1 spot, a mentor would I think.
I just suggested Grandpa Longneck as a mentor for the beyond rangers since he has spent most of his live outside of the great valley. He may only be living there due to his grandson and mate. We also do not see him a lot in some episodes or movies so maybe he visits where the beyond rangers hq is, if it is in one of the stone mountains that wall the great valley.
Just my opinions, not sure what the others think.