If you have a fancy schmancy character who isnt the main character, especially if you have multiples, someone's getting shafted.
there is no way around it.
You only have so much page room for storytelling, and if you cheat the system by PoV hopping, then grats you sideline the main character.
There was reply up top saying that a guide is really a character limiter, but that holds for all tropes and traits. The blank character sheet is the most powerful because it can become anything.
The moment you give it form, however, you fix its shape.
Everyone loved the old Luke Skywalker but he will never, ever become anything other than a male man who has magic sword powers, a dead mom, a dad who was evil until the last second, and a robot that beeps at him every so often.
He will never be a woman, nor a medieval wizard, nor a police officer in downtown Chicago.
And that's fine. In fact, how his limitations interact with the world he's in Makes him cool as hell. (well until the sequel trilogy but thats Disney's fault.)
Guides do get overused because you have a world with a "unique" magic system (usually not that unique, and I say that as someone whose magic system I feel is a little more nuanced and distinct than most.). Authors need a way to share this detail with the reader so they can interact meaningfully with it without the reader going lol snore okay thats cool wheres the next Deus Ex Machina.
Guides handle this in the most direct fashion possible, especially with a protagonist who knows nothing of the system. (in fact that pairing is the most common for a reason)
Then people, much like in real life, forget that guides are people too.
And if they didn't, then guides wouldnt feel sidelined so often, huh?
(hell, even if the guide doesnt just blindly follow the MC it would be a plus)