For starters by power levels I don't mean a flat number because we all know it's pretty much impossible to do so for the Touhou universe. What I meant was a way to see whom is stronger than whom based off of combat skills and magic proficiency. For instance let's say a fight broke out between our lovable idiot Cirno and the annoying as hell Tewi, who would win? Would Tewi because of the traps and trickery she can use or would Cirno because she can just freeze everything, INCLUDING the air inside someone's lungs. Reason I bring that up is because Cirno's power is the manipulation of cold which is NOT true cyrokinesis. She can control the temperature of things, adding or taking away 'coldness', including the air inside someone's lungs thereby choking them essentially.
This is exactly what we're talking about. You cannot measure powerlevels in Touhou. At all. There are very abstract and purely theoretical categories, such as one could easily say Yukari is more powerful than Tokiko, but such statements are obvious to anybody and are therefore pointless. Once you get into areas where the differences are no longer obvious to everyone, powerlevels and theoretical fights collapse into unintelligible mush. Abilities are interpreted any which way because you take advantage of the ambiguous semantics of things like "manipulation of cold" (such as what you're doing, which has
no basis whatsoever), you start speculating that Tewi can set traps and thus gain an advantage, etc. No, it's
literally impossible to decide on an outcome. Very rarely in the series is anyone ever shown explicitly using the "limits" of their abilities, and
no characters ever battle without restraint. That is the very point of the danmaku rules, and considering most battles are done as danmaku, there is nothing to work with. Abilities tell you nothing, danmaku and in-game appearances tell you nothing, speculation on theoretical scenarios and battles tell you nothing, descriptive canon material tells you little. This is why there is no "scale". There is nothing to measure.
You can have doujinshi portraying these scenarios all you want, but any real answer is not founded on any facts; it's just the whim of the writer who wins and who loses in any given scenario.
Now, with the WIN 98 characters, well just because they don't have personality doesn't mean we can't give them ones right? Hell Momiji and Dai were just midstage bosses with no dialogue but fanon gave them life. Why can't the same by done for the older characters? I don't see any reason why not...I also don't see why either. Jokes aside though aren't they also Touhous as well? Why should they get the short end of the stick just because they're older :wat: .
They get the short end of the stick because they're all largely uninspired and have little resemblance to the current cast. Dai and Momiji also had the advantage of being grouped together with other characters and settings and actually fit in the world without any effort. Sure, you could give the PC98 characters a personality and a setting and relations with other characters, but this is essentially just the same as shoving in an OC. I mean sure if writers want to then whatever cool, I mean Stuffman even has a brilliant ongoing interpretation of the Five Magic Stones, but there is no real point to giving these characters life, especially when you have so many others to work with. It isn't that they shouldn't be used as material, but they just likely won't get much attention for these reasons.
Onto Meiling, I don't see how, with the little dialogue she has had, she is stuck with the persona of being silly and incompetent, having a GATEkeeper when everyone can pretty much fly is pretty silly and incompetent.
The job of gatekeeper itself is a joke on ZUN's part, just the same as the border to the Netherworld in PCB. She's shown as silly and incompetent probably because of her awkward dialogue and inability to keep the player out, and it just expanded from there (PMiSS into IaMP etc); there doesn't have to be a huge reason why a popular interpretation catches on, and there isn't really a problem with that.
If you need security like that just make your own security force, one person who specializes in martial arts can't really do much against flying people who specialize in a type of ranged combat that they invented. Either way is Meiling is so useless why keep her around? There has to be a reason right? If you were in Remilia's shoes and you needed security for your mansion and your gatekeeper was about as useful as a scarecrow wouldn't you replace her? Of course you would.
Her background isn't explored very well, but while I think there should be a reason, there doesn't have to be. That ambiguity is part of what makes Touhou wonderful; you can go write a story about how she became the gatekeeper and you probably won't be stepping on any toes. I'd say that Meiling was a part of Remilia's "army" heading into Gensokyo in the Vampire Incident. She might have been together for longer than the SDM's move to Gensokyo, but meh, the thread of evidence stops there.
I'd say Meiling AT LEAST has some relations with the dragons, I'm not saying she is a dragon now, I'm just saying that she has, at least some form of connection with them. If spell card rules are thrown aside then I'd personally think Meiling be one of the strongest in Gensokyo.
no basis whatsoever, please explain how you come to this conclusion besides a chinese martial arts theme to her character and the character "dragon" on her hat
Lastly Reimu, that plot armor so thick you try to cut it with a knife but the knife would melt in your hands (see: plot armor). It's canon that Reimu doesn't straight up win each fight, she has challenged people to rematches until she has won (yes, she has used 'continues') so she isn't as omnipotent as most people make her out to be (Hax sign: you just plain F***ing lose is a good example). So less OP Reimu more fair fights.
I'm not sure what standards you're using for "plot" but Touhou doesn't really have any. Your definition of "plot armor" is essentially "the only endings in the games are when Reimu wins" but that should be utterly obvious to begin with. It's nonsensical that you can call beating the game "plot armor". I might even argue that mentioning she asks for rematches is evidence that she
isn't overpowered, since it means that she does lose. You only notice that "she wins every time" because it's a required consequence of clearing the games.
Reimu didn't make up the spell card rules on her own, the rules don't say that she will eventually win, and they don't mean she can boss everyone around. Her role as the Hakurei Miko is what everyone else has to make note of, since she keeps up the Great Barrier and so you have to avoid killing her. Which would be pseudo-plot-armor, except, the spell card rules were created partly
for the purpose of letting people win against Reimu. The implementation of the rules are like, the utter opposite of giving Reimu plot armor.
P.S. Mokou's hair is violet not white. 
Coloration in shadow doesn't make it widely accepted. As far as I know there isn't any source saying she has purple hair, and the description on Touhouwiki is just looking at her portrait and going "ok I see purple in there". If any color besides white, people usually use gray or pale blue. Without any real support you just have to let that go to the fan decision, you can't really correct people on something without extra evidence.