Well, I wouldn't say that. I simply offered what I thought might have been the cause. I have no idea why it was deleted or who deleted it. So I'm not explaining on anyone's behalf.
Ultimately these things are at the mods' discretion, and whatever they say is what goes. Believe me, I've had posts deleted/moved/altered, and sure, they might be posts one took time to make, but it's not up to us to challenge their decisions. It's just how it is.
It rightly isn't, but the creator of the video I linked has experience in character design as a profession. I take the word of a professional as a highly informed opinion.
Maybe the way he presents the topic can come off as a bit condescending, but that tone is in no way directed towards the audience of the video, rather the designers at Riot Games that he feels compromised artistic integrity.
And truthfully, I believe he makes a good point. When sexualization (which is a tool of character design and not inherently good or bad, as he explains) is used in such a way that the aspects of the character cannot be clearly gathered, it is to the detriment of that character.
He uses a great example in the video (and it's arguably his strongest one) where he points to the one character that's supposed to be a high noble-woman and a town sheriff (forgive me, I don't play LoL). Instead, the character designers at Riot chose to use sexualization in a way in which the qualities of high nobility, lawful justice, order, structure, etc. are not clearly seen with a glance at the character (which is a goal any good character design should strive for).
MOCing is in essence character design, and because of that I'll hold the same standards to it. The problem pervading female MOCs isn't the use of sexualization, it's improper use of it to the detriment of the character. Very few of these hyper-sexualized MOCs actually have sexuality as anything to do with their character, and to that end any character traits they do have aren't easily seen in the design without reading a lengthy bio.
As the creator of the video explains, it's okay to have sexualized characters, and it's okay to have sexualized MOCs. Some people want to express those kinds of MOCs as a piece of art. Some people see that as a desirable and/or artistic quality, and others do not, but that isn't a problem with sexualization, it's human nature.
The problem comes from MOCs that use this design tool when it doesn't fit the character, and again, it's a problem only in that we want people to make the best MOCs they possibly can, not because of their design choices.
It's an especially slippery slope for Bionicle MOCs considering their biomechanical nature, and the fact that sexuality and sexual attraction aren't real concepts in the lore of Bionicle. Thus, it's a bit weird by definition to include sexuality as a design choice, but it can be done. Roodaka comes to mind as a character that uses it well, as it fits her character of being a seductress. Yes, it's weird for Bionicle, but it had merit to her personality.
It just has to work with the character.