I want to put this out there first: Onesurvive, I like your art style. It's something different from what you usually see and I appreciate that.
My personal opinion on Mara's post is that HOW he delivered his message maybe went a bit overboard...but, all the same, I understand what he is saying and I'm worried you don't understand it. Here's the thing: the art you posted the other day, and the artwork you shared with us in February, looks like it might as well have been made back in 2009 when you made the very first post in this thread. (EDIT: I'm just seeing now that the first page has been edited...and there is a "2014" on one of the pieces. So have you gone back and edited that first post from 2009 with newer artwork? Because if so, then nevermind.)
Now, in some ways, that can be a good thing. It means you're consistent. You picked a style and you're sticking with it.
I think what Mara is trying to say is this: 10 or so years later, ideally your work should look a bit different. But I'm seeing that the colors, for the most part, still look flat and the shapes still lack depth. If I were you and if I wanted to improve, I would focus on experimenting a bit. Try a different color palette. Experiment with different shades of the same color in one part of a Senshi fuku that's supposed to be one color. Consider trying new ways to layer a character's hair.
I think Mara is just comparing your art from 2009 (again, it's right on the first post of this thread) to your art from 2018 and is seeing that it has the same overall "issues" though some might find them charming. I'm in the middle myself. I like your work and it's certainly better than I could ever do. I think you're talented/skilled and your style in portraying the Senshi is really bold. But it would be nice to see finer details.
Mara said some unnecessary things but overall, his critique shouldn't be completely thrown away just because it was quite harsh. There is value in that. When I was writing, especially back in college, I spent a lot of time hearing other people deconstruct and critique my work, sometimes in extremely harsh ways. It's painful, but there is a lot of value in that. I hope you can take the core of what Mara is saying -- that 9 or 10 years should generally show more improvement than the examples you've shown -- and consider what it really means.
Of course, you might have improved in other ways we haven't seen. But I definitely think that the artwork you've shared on this thread from 2018 very closely resembles the artwork from your first post in 2009. I don't think the artwork is bad. It's charming. I think it could just be a lot more dynamic.
EDIT: And for what it's worth, I love your Suited Sailor Senshi. I think that when you really learn how to utilize small details to enhance the larger image, your work will be truly fantastic. But despite the relative flatness of your artwork, I like your art direction.