Mikoto is basically the root of this recurrent issue. The problem is the fact anyone reading/watching the series should see that her different types of attacks don't have the same power behind them. Simply compare the damage she causes using her magnetism to throw metallic objects to the damage she causes with a coin Railgun or with her electricity, despite all those being valid attacks. This also applies to her L6S state. We see that some of the attacks she uses then are her picking wreckage with magnetism and throwing it at Touma and Gunha, and we see that when she throws individual pieces of wreckage at Touma they clearly don't have the same amount of power that even the coin Railgun of her weaker base form has despite being much larger objects launched by a much more powerful form. So there's an undeniable difference between the kind of AP she produces when she uses just magnetism to throw things that when she uses a Railgun, even when it's a stronger version of herself.
As for her other L6S stuff, her lighting attacks are easily dealt with by Touma and Gunha in that form, and all we know about her iron sand is that it's stronger, given she doesn't use it much in this fight for attacks. All that we have left then are the weird energy attacks, which have the feat of launching Gunha far away when taking him by surprise (which we now know from Astral Buddy lowers his defenses significantly) and temporarily disabling him by putting him into a wall offpanel without giving him serious injuries. So yeah, considering Gunha has a anti-electric forcefield that already scales to L6S Mikoto's electric attacks, what we could do with this fight is scale Gunha's higher Durability ceiling to the energy attacks and his power's AP to her iron sand shield, but I don't think you'll get an upgrade from those given the lack of feats.
So the obvious issue here is with Mikoto's lightning. The calcs for Mikoto's lightning make it much stronger than any of her other feats, so obviously people want her other attacks to scale to it. All her other attacks consistently perform at a much lower level so the lightning is the clear outlier. The only thing that comes close to implying the same level of power in the novels/manga is a throwaway mention in OT1 that her coin Railgun can take out a nuclear shelter, and none of her coin feats or stronger Railguns reflect that. In the Railgun SS3 a reinforced wall of an AC building manages to tank it, bringing even that lone statement into question. Her electricity is much like real life's in that it has a lot of energy compared to the actual physical damage it's going to cause. Hell, in Railgun SS3
Hinadori Hanakawa attacks her by puppeteering biker suits made of leather, and while her multiple casual lightning attacks don't cause them any damage besides burning the suit's leather, once she figures the suits are empty she uses her coin Railgun to easily obliterate the two suits since they are just biker suits and being able to resist electricity doesn't mean you can take technically weaker piercing physical attacks, because electricity doesn't work the same as physical projectiles moving at high speeds to pierce a target, even if they both use the same power source (Mikoto).
I am of the firm opinion that Mikoto's attacks should not scale to the calcs for her lightning without significant feats and evidence that proves otherwise. Thus I think that L6S should have a clarification of her other attacks not scaling to her lightning and instead having 8-A iron sand and energy attacks.
For Gunha, he should scale to the higher ouput of Mikoto's iron sand, yeah. I agree with him being 8-A. Although he needs a revision in general given Astral Buddy.
As for Kakine, the best feats Kakine has in OT is easily defeating Mugino offpage and slicing a building in half vertically with his wings. That's pretty much it. He shouldn't scale to Accelerator in terms of raw power, because the fight is Accelerator overpowering him a couple of times and Kakine tanking being launched into buildings and such because of his power, followed by Kakine adjusting his DM to bypass Accelerator's reflection. A few clashes later Accelerator adapts his redirection to Dark Matter and stomps Kakine in a single move. This doesn't imply power parity, it implies the weaker character putting up a bit of a fight using smarts/trickery/hax and what not until the stronger character decides to end the fight and stomps the weaker character.
In NT he clashes a bit more evenly with Rensa when she's using Accelerator's powers and only gets defeated when she pulls out the black wings and he takes a hit for Touma, taking him out for the rest of the fight, which is why he currently scales to her.
I personally have no issue scaling Kakine to 7-C, but he lacks feats in that kind of level so it would be just scaling him to Mikoto. Like, assuming it was a reference to her even the comparison he makes in the DM manga is about his wings resisting a railgun blast, because the story still treats it as her strongest attack despite feats demonstrating otherwise, just like it still pretends an arcade coin going at Mach 3 is supposedly impressive. And for all we know, if the two were to fight Kakine would just make his wings completely insulated and just 'lol nope' all her electric attacks (don't take this last sentence seriously, it's just a theory as to how it might go if written by Kamachi).