@Danios15 No. They're not the same person. If you spend time watching Fate (sorry if you have), you'll see that show is more likely derived from the original Winx Club than being a faithful adaptation. Though I'm a bit curious why you're looking for it from Powerlisting Wiki.
I'd like to make it clear that it's not my determination or anything. People often forgot this place is a wiki, it acts like an online encyclopedia, from fans for fans (though I'd be happy if Mr. Straffi or Viacom or Rainbow sparks an interest in affiliating with this humble place). As a wiki itself, we need solid proof for matters to be stated. The origin of the question must have been someone asking WhiteJasmineFlower about which episode/movie/comic/book that Luna is stated as a fairy as they failed to find to check (you may want to check this matter with her as I only assume it from the scene) and none of us so far has been able to point it out.
I must have been misunderstood that you were trying to imply/stand up for the content that Luna is a fairy. Still, what you pointed out about the sun was just hinted/implied or understood by fans, you (even I myself agree to this hint) but we have no solid proof to keep this valid I checked on Italian Winx wiki and they listed her as a fairy too but they pointed out no references. Funny enough that I talked about Tecna's mother in the previous reply of mine, and in the Guide to magical world book, she's stated as a fairy. I tried to find if they mentioned about Luna being a fairy or not but I found nothing. I hope I have made myself clear enough about the matter and the situation of the debate/conversation to prevent further confusion.
I do not know why the conversation is directed to "transformations" now (as I only stated that the Guide book above failed to provide better content). About season 8 Sirenix, as you said you heard, I believe you didn't watch the season or the specific episodes that feature the transformation? If so, I'd like to inform you that no explanations were given about the changes of appearance. The only explanation is how Crystal Sirenix comes up (the Sirenix power reacts to magical ice so it evolves and protects the Winx [from the cold].)
For the rest of your theory, it's clearly interesting but I'm afraid this is not the place. You may want to create your own thread/discussion and put content in. I believe many people, including Anon himself will take part in. If you're interested in discussing this directly towards me, you can just leave a message on my talk page. Though I'm not sure if I can get back to you anytime soon if it's not heavily wikia-related, I'll try to give a reply if I have time. I'll just give my thoughts about your theory. If it by any chances offends you, please consider it as my blunt thoughts (though I have already done my best in considering with words I should pour out).
For Roxy's transformation, it's Believix. No hybrid. I do not know how people think but if I'm a creator of something, then any side-information provided by me should be the truest, absolute answer. Many official materials directly from Rainbow stated her transformation is Believix, whether there's a plothole or people can accept it or not.
I'm not quite sure if I get what you meant about Sirenix changed after it got cursed. Just pretend that this theory is correct, and season 8's Sirenix should be the true form of Sirenix (before it was cursed), then after Bloom made her wish of removing the curse on Sirenix by the end of season 5, the Sirenix transformation we saw in early season 6 (before the Legendarium absorbs all the girls' powers hence they have to earn Bloomix) should be the designs we see in season 8, shouldn't it? But in fact, it's not.
Yes, I agree about the part that the transformations we see on Miele, Diaspro are pretty much the same with basic form (let's just call it Winx form) of any student at Alfea. But the point is, the name could be different. Let's take a sample from real life. Everyone knows about pandan leaves (if not please search for it ;;u;;). It's called "pandan" in many languages/countries (even any Latin-root language keeps the root "pandan" then the variant name comes after), but my country, and China (sorry I do not know many) call it with different names. So at Lynphea College they can call the Winx form as Sparkly fairy form (just a random name so I'm sorry if it sounds dumb) and in Eraklyon Institude they can call it as Precious outfit... Back with the mentioned content above, it's just my theory/belief (or people often say -- headcanon) and no solid foundation so I don't have this available in any article.
I partially agree the part "Another thing is that every Fairy Form is apparently subconsciously shaped by a mind and looks of its bearer" and "Another thing is that every Fairy Form is apparently subconsciously shaped by a mind and looks of its bearer" as seen by Bloom's Dark fairy form. Honestly I think being corrupted by dark magic is just an excuse. After being corrupted, her personalities changed as well as fairy form (but even her irises change) so clearly Dark Bloom is not happy about sky blue, sparkly fairy outfit and blue eyes that Bloom posses, hence the change in mentioned features (which please Dark Bloom).
Sirenix and other known transformations have never been stated as "higher fairy levels", it's just stated as "powers". The only higher fairy level mentioned (again) is Believix. Actually you only need Charmix and Enchantix if you ever enroll Alfea (for the purpose of graduating), otherwise honestly as a mere fairy in the magical world, I think the obtaining basic fairy form then move on with whatever powers is enough. People often say about Bloomix being impossible to obtain as there's no Dragon's Flame spark around. True. But have they considered Sophix and Lovix? There's no Ethereal Fairies around everyday to grant you Gifts of Destiny to have them. Same with Tynix, you can't be certain if you fairy animal can grant you a bracelet containing the power. Mythix, Butterflix are actually the ones I deem possible as you can earn them, not being "granted" by someone because if they die then no one is there to grant you the power?
I also see Sirenix as power (not a level) not only because people constantly mention it as "power" during the series, but also because being a fairy power, even witches can earn it, after being granted.
The last thing, only little related to your theory is that you mentioned witch forms. As Mr. Straffi is interested in making a spin-off about the Trix and exploring the world of witches (finally, after an eternity), I hope we can learn more about witches transformation(s) and how the witches view fairies (and if possible, fairy transformations) as so far, the Trix is the only ones transforming to basic witch form. Minus the transformation they transformed to in season 6 and the hybrid in season 7, the other transformations they earned are all granted by notorious villains, making these may not accessible to normal witches, or these are not even legal witch transformations that a witch academically is trained to earn.