Some thoughts since I find opinions on AC so interesting to discuss.
Denzel is as much a plot device as Marlene is a plot device in VII.
Both exist as lenses meant to reveal the inner conflicts and emotional ties their respective caregivers carry into their battles. Aside from that, they are not showcased often or in-depth. Usually it's in relation to
another character they relate to. Marlene to Aerith, and Denzel to Cloud.
The only difference is Marlene originated in VII and Denzel came later. Denzel has the benefit (and curse) of coming after the game and being depicted in a modern medium with voice acting, higher definition, and his own story.
Objectively speaking, I don't see how one is more hollow or defined than the other. Denzel isn't shoehorned as some super special kid above the others, nor is he so superfluous that removing him from the story leaves it more streamlined and focused on its core plot. Denzel represents someone that Cloud and Tifa care for because on one hand they share the fate of being victims of Shinra, and on the other, Cloud and Tifa in a twisted way, are responsible for his parent's deaths too. He's a promise of redemption to both of them. Denzel also gives some uniquely appreciated and needed pathos to Cloud and let's him showcase another side to him that is rarely seen in modern depictions. Cloud, Tifa, and Denzel make up a family. The additional scenes added with him and Marlene interacting with Cloud make the film better and give Cloud a far more holistic and in-depth depiction than "depressed young man who turns badass during the later half of the film."
I mean, if you remove the kid(s) from AC (especially Denzel), then it all
really falls apart as a movie and story because now it TRULY becomes a question of "why?"
What is the hook here (aside from the obvious?) Who are the people Cloud, Tifa and the others are caring for? Who are the target audience of Sephiroth's
delinquent teenagers remnants in trying to further build up hatred for the planet? Why is Cloud's beef with Kadaj personal, aside from an uncanny resemblance and Kadaj's stalker-like tendencies?
I mean, in the end.. a lot of the ways people want to change AC essentially destroys it to make something else entirely.
Which is a fine and valid opinion to hold, obviously it's not gonna appeal to anyone. But if the premise is to
change AC, we're to at least accept AC's existence on its core premise. Which is a movie focused on Cloud, his relationship with Tifa, moving on from the past with caring for the orphans with Geostigma, and
of course Sephiroth's return. Otherwise, you're basically making a brand new FFVII movie.