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About the "kwamis as mentors" angle: Interesting to read and analyse, yet I can't help but feel they were not necessarily meant to be seen as mentors. At least to me, they seemed to be kind of whacky mascot characters who are tied to the lore, who have a personality to crack a joke or point something out or cause a little situation or be cute, but nothing more.
They are rather naive magical entities chained to jewelry (a fact they don't seem to mind that much or think about at all except for Plagg) and all that talk about "being around for 5000 years" and having seen many holders before is just there to make them seem more wise than they actually act like. From what I've seen on the show I would even assume there's a threshold to how much they can even mature emotionally and understand humans. Sometimes Tikki and Plagg even come off as indifferent and egoistical towards their holders (like an example you gave with Tikki, or Plagg's fixation on cheese over Adrien at times).
So...sorry if I missed it, but why do you view them as mentor characters? You made an interesting post about rom-com vs magical girl and the magical girl part is exactly why I always viewed them just as critters to appeal to kids, but nothing more. I can see that the show's writing is so inconsistent that sometimes they are portrayed as wise but more often then not they are just background noise to get a little interaction on screen so that the characters are not talking to themselves about miraculous stuff or to point something out for the audience.
The show's writing is pretty weird, so there are elements that are hard to get a clear read on. The Kwamis are one such element. When they're one-on-one with their chosen, they often feel like mentors to me. When they're all together, they almost always read like "critters to appeal to kids" (mostly because there are too many of them to let them have individual personalities when they're all together). So while I think that they're supposed to be mentors, it's not like that's the only canon-accurate read.
To dig into what I mean by the one-on-one writing, let's look at this exchange from Feast:
Master Fu: See, Wayzz? If Marinette had kept her Miraculous, the sentimonster would have swallowed her right up. Wayzz: Or she would have transformed into Ladybug and fought it. Master Fu: Sometimes fighting is futile, Wayzz.
And then later on we get this:
Wayzz: Master, look! Ladybug and Cat Noir, despite their ridiculous costumes, they haven't let you down! Wang Fu: That's impossible! They don't have their Miraculous! Wayzz: Master, it's obvious it's them—who else would do something so crazy? Cat Noir (Adrien): Hey, have a taste of this! Some exploding banana split from Bananoir! Ladybug (Marinette): Much tastier than any Miraculous! Wayzz: Look, Master, there's no use in running! Your disciples never give up the fight, no matter what! With or without their Miraculous, they are Ladybug and Cat Noir!
That's some pretty active mentoring right there.
Wayzz is probably the character that feels the most like a mentor to me. When he's with Fu, he feels like Fu's partner or adviser, which is why I think that the Kwami's aren't supposed to just be cute critters. They're regular ol' Jimmy Crickets meant to act as a conscience that the characters can talk to since this is visual media and you want a way for the characters to talk through their thoughts instead of having them do it all internally.
I also present this exchange from Desperada as evidence:
Adrien: Plagg, Ladybug needs me. She needs "Adrien"! Plagg: If you asked me, this whole idea is worse than cheese in a can. Adrien: She thinks I'm the perfect guy for this mission. Plagg: You can't be Cat Noir and another superhero at the same time! Which means that you're not the perfect guy for this mission. Adrien: The Lucky Charm told her I am. Plagg: That's not how it works. Why am I bothering? You're not even listening.
We then get Plagg reiterating that this is a bad idea through multiple loops, ending with this:
Plagg: Ah! At last, you've come to your senses. Adrien: I'm not sure Ladybug will have very fond memories of her experience with "Adrien Agreste". Plagg: Then make up for it as Cat Noir.
See? I told you Plagg can be a good mentor when he wants to! Tikki, take notes!
I'd even call this bit from Sapitos some quality subtle mentoring from Trixx:
Alya: Oh please, Ladybug! We'd make a great team! I could help Cat Noir and you every day! Ladybug:(her earrings ring) I'm about to transform back! Hurry! Alya: Please? Ladybug: I have to go! I'm trusting you! (opens a nearby door and goes inside, so she can detransform) Trixx: You're absolutely right, Alya. I'm sure the three of you would make quite the team! You have all the makings of a true superhero. You're strong, brave; but most of all, you're trustworthy.
Way to both build Alya up and reminder her of her duty, Trixx. Gold star. Quality mentorship!
So are the Kwamis supposed to be mentors? Who knows! I just see them fill the role often enough to feel comfortable judging them through that lens.
Miraculous also isn't the only magical girl team show to make the cute critters into mentors. That's a pretty standard path even though it's also common to see the critters used to sell merch/appeal to kids and nothing more. In terms of classic magical girl team shows, I'd say that the Kwamis are written way more like Luna and Artemis from Sailor Moon than Mini Mew from Tokyo Mew Mew.