You are correct; if analyzed, every artistic movement and style could be found to have similarities and consistencies. This is how we define artistic movements and styles throughout history.
If a category exists, there are defining features in which art can be placed into or out of the category. It's about point of view and opinion, about what the audience chooses to notice, which artists will never have control of.
I don't consider myself a manga artist, though I'm happy to have the support of the manga art audience, so this not a personal concern. Not looking to defend or argue for a cause, simply tossing an opinion into the mix for fun. You all can take it where you want into discussion, but leave me out - I did not expect attention from such a brief comment!