Beware! Spoilers towards "Megalobox", "Tomorrow's Joe" and "Million Dollar Baby".

General impressions:
So, the story is lacking. It’s decent at best, even if you are not comparing it with “Tomorrow’s Joe”. But IF you compare - then this story is just straight embarrassment in front of its predecessor.
Being inspired by “Tomorrow’s Joe” in this work just looks like copying the whole story and trying to compose it into 13 episodes. So to call this story a “reinvention”, “reinvention” or “successor” is just impossible.

About the concept:
Intention to add gears to the story is another, so liked by the anime, idea of “let’s add some cool-sounding concept just because we can”. Yes, the whole story revolves around the gears, so it’s the important part of the plot, but nonetheless introduction and realization of this concept just takes away from the boxing spirit and doesn’t enrich the story a lot. So with such “thoughtful” implementation they just shouldn’t add gears.

Why though I don’t like this concept this much? Well, firstly - the ideal and spirit of boxing is that you are able to become a successful champion without any money basically. That’s what almost every boxing story revolves around. That’s the sport for the poor, for the outsiders, for the delinquents, for the outcasts. But introducing of gears makes this sport a lot more akin to some cycling or racing, where you in first place need equipment (consequently you need sponsors and money), and only then you need... well, yourself.

And yeah, there were some plot correlations with this “boxing spirit”, when Joe was fighting opponents without a gear. But first of all, he’s the exception, and the sport in general became a lot more relying on the money in this world. That’s already some form of the desecration in my opinion. And second of all, he’s still had to wear gear when he met the opponent of matching skill. And honestly, yeah, no wonder, it’s funny to try to fight a cyborg as a human, competitively.

About the plot:
So, plot is a general story about underdog and his friends that, despite everything, are climbing up in their fame and social status. Using only their willpower and character, without any ability to rely on money or connections.
That's basically the entire plot. We don't see the dire implications of boxing on one's life and loved ones as we do in 'Tomorrow's Joe,' nor do we get as deep a dive into a boxer's path and psychology.

So the problem is - this is just a cropped version of a “Tomorrow’s Joe” message. And that’s quite logical outcome, because authors just took the “Tomorrow’s Joe” plot and tried to trim it up to 13 episodes. They shouldn’t try to do this in the first place. This was a doomed battle from the start.

Inference:
At the end, you can compare “Tomorrow’s Joe” with a serious and deep story, as in the movie “Million Dollar Baby”, while “Megalobox” is a kids’ version, which can be compared with, maybe, “Rocky”.