<PERSON> and <PERSON> are archetypal examples of the "spiritual guide" - the knowledgeable elder used as a device to reveal wisdom to the protagonist (and the reader) as the story progresses.
In Star Wars, the reason these characters don't simply fight all <PERSON>'s battles for him, is that even they are not powerful enough to defeat the enemy. It turns out, <PERSON> is destined to ultimately grow stronger than his guides and to do that, but they have to die along the way while facilitating his growth, and it is <PERSON>'s development upon which the whole story is pinned.
This is much the same in Harry Potter, in which <PERSON> is super-powerful but ultimately <PERSON> is more so and <PERSON>'s role is to facilitate <PERSON>'s growth, and impart his wisdom to <PERSON> until such time as <PERSON> is powerful-enough to do the job himself.
Another classic way a of limiting the impact of an all-powerful superhero character, is to give them a profound and fundamental defect. <PERSON> is an example, whose ankle was not invulnerable, unlike the rest of him. But this might equally be a mad genius or an alcoholic father or whatever. <PERSON> was once mighty and still is, but he is an old man and no longer fit for embarking upon quests - the same with <PERSON>. It's a great scene where <PERSON> reveals his incredible Jedi fightings skills, even as a frail old <PERSON>. But his days of physical combat are over, really - by now he thinks, guides and teaches. Same with <PERSON> in X-Men - he has a brilliant mind, but his body is useless. These paradoxic characters are interesting because we marvel at them in real life - see <PERSON> or <PERSON>.
Another method of sidelining your mentor, is to give them some huge battle to fight. 190
This is seen in Lord of the Rings, where <PERSON> declares "You cannot pass, flame of Udûn" to the <PERSON>. Then cries "Fly, you fools!" to the party as he plunges into the darkness below, after the <PERSON>'s whip catches his ankle. This serves to disappear him for a good while, returning later as <PERSON>. In a way, one might liken this to <PERSON> battle against <PERSON> in which he dies, but instead of returning later (aside from as a glowing ghost), <PERSON> takes up the spiritual guide role where he left off.
Where you talk of having "flaws and character arcs", multiple bits of paraphernalia sounds woolly and confusing. It's going to detract from your protagonist's journey if a load of nonsense is going on with the mentor. Better in my view to have one almighty awesome kaboom that leaves us in awe of them, or perhaps something dark and mysterious - maybe they have a bigger battle to fight. But who knows and who cares, as long as it's simple - this isn't the mentor's story , it's the mentee's.
Another device you coudl use, is to make your mentor entirely powerless other than acting through your protagonist(s). How about you keep your mentor at bay by restricting their communication with them. Maybe the mentor comes to them in their dreams and they only catch snippets of what he is trying to lead them to. Then part of the story's mystery is working out where (s)he's leading them. 190