Let me be serious for once, it doesn't make sense that Imu has no protection whatsoever so her having a personal guard make sense. We can expect the world leader to have a personal guard composed of character stronger than yonkou by quiet the margin since Luffy already beat a yonkou. The film red kind of solidify my idea since the first thing the gorosei think about while learning that shanks has a daughter is "is she from the fearland family?".
1. Already wrote a theory on this before. The human being you are referring i stated to be coby. Failed experiment from vegapunk that happened to have pink hair like momo fruit so he deemed the experiment kobh a failure
2. Make better vinsmokes and then what? That is vastly inferior to what the Seraphim are. They are augmented, have genes of previous others, and have devil fruit like ability without a devil fruit. What yoi are asking for is an even weaker version of what vegapunk has already made. Hence why the only step up would be added what you stated and having more powerful super suits that can be coated in seatone,
No the only difference between what you suggested and what I suggested is that I like the idea of upgrading the people on a cellular level which avoids changes to character design where as you want everyone running around in Ironman suits. I don't care about any previous theories you've come up with, and there is no way that what I'm suggesting would be inferior to the seraphim who are mindless and simply follow orders. If there was a way to upgrade regular people to the level of the seraphim you could upgrade people who already have their own logic, reasoning, combat experience, and a will of their own allowing them to use haki which the seraphim can't because they have no free will. Litteraly the only differences between what I suggested and what you suggested are that you want the power up to be in the form of a gay ass super suit that would force oda to change the design for every character wearing one, whereas if the power up comes from a serum or a perfected artificial devilfruit the power up happens on a cellular level which avoids oda having to put everyone in some lame power ranger suits. The possibilities of what all the power ups can do is irrelevant to this discussion, I'm merely pointing out that power suits are a temporary and inferior option as opposed to something that would be a permanent boost.