I'm really not feeling these latest developments tbh. Maybe they'll be better when its done like some of the other weaker arcs.
Like are we really supposed to just take it at face value some script writer also managed to be a super scientist, whose 10 year old clone overpowered 4 adults and made a secret lab base? What?
Also kinda lost track of what Chidoris motivation even is, but whatever.
No, we are supposed to take at face value that he is a writer who is acting and playing the role of a super scientist.
Because he isn't a scientist doing any real science. He is using the divine dragon energy to change reality to what he has imagined. He imagined a story where he played a mad scientist, and the divine dragon made that reality.
The original Shinya said it in Chapter 167 when talking about creating the cloning tube to clone his son:
My own contribution is insignificant. The whole reason this exists at all is thanks to the power of the divine dragon. And how "divine" it is. If we can control this power like this we should be able to fulfill any desire we have.
And Death Messiah was where the manga previously showed us that is how divine dragon power works. Death Messiah was able to make his dumb OP fan theories reality just because he imagined those were the powers Death Messiah was supposed to have. As long as he had access to the divine dragon energy to do it, which he did via the clones. See what D said in Chapter 120 when the Green team were talking about Death Messiah's powers:
Unclear who is initially speaking, probably D: Huh? Death Messiah can read minds?
Hisui: That's dumb. Are you sure he's not just listing random nonsense at this point?
Chidori: He is in fact, very serious
D: He's Dumb
Chidori: He truly believes that the all-powerful Giga invader he loves should be capable of that much at the very least.
Hisui: Could it really, then?
D: It's a character from the Tokusatsu right? How would I know!?
Chidori: Deluded as he might be, the question is whether he's making that delusion a reality.
D: No... He had it. The Materials to bring any stupid delusion to life. [Next to a panel showing the Yumeko clones]
The story going on for Ranger Reject is actually quite meta. It is about a power of a divine dragon that has the ability to change reality to match imagination, or more specifically in this case a story. You just have to be able to access that power. Which is currently shown to be done via the bloodline of the divine dragon priestesses, although we have no real firm explanation of exactly how or why, yet.
And that was used by the evil new Shinya/yellow ranger to alter reality to make a super sentai type of story reality. That was what Shinya/Yellow did, and that is what his flashback showed.
It is important that he was a writer for this, and not a scientist. A scientist could not actually do the things he has done. It was not done through science. It was done through the divine dragon. It worked because he was able to use his abilities as a writer to more firmly and clearly imagine the story that was used to alter reality.
That is where Chidori's motivation and plan comes in. He is trying to end it, but he knows he can't just do an action from within the story to try to end/change it. New elements that are introduced to try to end the charade, such as the Neo-Rangers, can't actually bring it to an end. The story, and thus reality, is just adapted to account for them as part of the story and continued on anyway.
Chidori is trying to end it by actually providing an ending to the story to stop it. Specifically an ending based on the original script for the end of the original TV show. The phantom script. That was also why Yellow had been searching for the Phantom script, as he new it could be used as a basis for ending it all.
That ending appears to involve one of the rangers (not sure if it had to be Green specifically) betraying them and becoming the final villain. So Chidori is acting that out to end the story.
And regarding the evil Shinya being powerful even as a child? Again, divine dragon energy. Two possible sources for it. 1.) He was actually a clone of Shinya's dead son, not Shinya himself. Shinya just imprinted his memories onto the clones. And his dead son was part of the dragon priestess bloodline via the mother. 2.) He was cloned using divine dragon energy. That may also provide some kind of connection to the divine dragon since the Red Keeper clones are inherently superhuman in strength, speed, and fortitude despite having no known connection to the dragon priestesses. Something similar may be the case for the Shinya's son's clones.
Regardless of the reason for the connection, it is the Divine Dragon energy that allowed an 10 year old to kill a bunch of adults and create an evil scientist lair.