Okay, this epilogue definitely didn't need to be its own part, why they didn't just publish these last 16 chapters in the main serialization is beyond me..
Honestly, this was an underwhelming finale to me. The anti-proton bomb twist comes out too late and without enough setup, and it's not elaborated on how it was built and by whom, how exactly it was going to achieve the impossible task of destroying the whole planet when the Friend's engineers couldn't even so much as launch a single rocket to Mars. And this isn't the only loose end that remained untied, so many plot points feel underdeveloped, unrealistic or implausible in a world that tries to be grounded and fairly true to life. Like when the giant robot's engineer couldn't build it accurately to the unrealistic specs from the book of prophecy so he had to resort to smoke and mirror tricks to make it work, but then later he actually does build a fully mechanized working recreation of it like it's some kind of sci-fi setting now. But at least he was shown determined to build it and developing blueprints for over a decade, the UFO saucers and the anti-proton bomb are not explained whatsoever, somehow they just work. And nobody even investigated whether or not the bomb was actually functional and deadly enough to destroy the planet, the entire world just ran with the preposterous assumption that it could but it might as well be a sham, we never do find out anything about it.
There are plenty other similar problems with the plot, like how Kanna's psychic superpowers got simply handwaved with the reveal that they're the result of some secret drug given to her mother during pregnancy which is such a lazy and unrealistic excuse. And then we get setups that end up completely abandoned and forgotten, like Takasu being pregnant with Friend's child didn't lead to anything relevant at all, and the story wastes so much time on mulling over that Mars emigration plan and making a big deal out of it but then it just gets abruptly dropped for other plotlines and when it's brought up again much later they just go "Eh, we couldn't do it. Anyway..!". This writing is just so unfocused, plus it spends way too much time on developing boring characters that don't do anything special. Way to end the manga on giving closure to the bowling gramps and his bowling girl of all people... I'd rather see it end with that trio of mangakas finishing their comic, they weren't even important or anything but it would still make for a better final page than what we got.