Yeah, the monsters are actually the biggest problem... superhumans are the response to the monster threat after all, unless we get some reliable soldiers to fight against the monster faction it doesn't matter wheter Ella or HERO wins their little feud the monsters will still come for humanity and destroy/consume everything. The future after that will be bleak anyway because the tech to make superhumans already exists and is now public knowledge, also Ella was already changing people underground for quite a while so believing that it's possible to erradicate the superhumans when a serum or a pill is all that takes to make a new one at this point is an exercise in futility.I don't think there would be an eternal power struggle, personally. There's only like 13 known lvl 5 superhumans currently(12 from HERO and Ella). We know Hero doesn't know about the Numbered(on the surface) and treat monsters who are likely below them as major threats. If a Numbered and their S Rank kin wanted to, they could probably wipe out most of, if not all of, Hero and humanity. The way I see it, a status reset for supehumans wouldn't change anything. Like Xanthe said to Clark after he reached lvl 5, if the monsters actually worked together, they would wipe everyone out. The world is going to be awful no matter what because the monsters are also increasing in activity.
Even if we went with your suggestion and got rid of superhumans or limited them, the monsters would still be a threat. They exist beyond earth in other planes/realms/domains out there in the universe. Humanity still would fall prey to them and as far as we know, there's no way to get rid of them permanently. At least from a superhuman/humanity side of things. Even Nico would struggle to enter a domain of Hex, so without superhumans in general, humanity would still be at risk of annihilation from types out there. I'm not sure what WW has planned but only a power black hole, for the lack of a better way to say it, would save everyone. Where all of the monster power and their genes returned to their origin and disappeared altogether. Whether that be from a superhuman going around and taking all of the power within themselves before self detonating or the Dark God coming and doing it. Beyond that, limiting superhumans wouldn't actually help humanity as there would still be monsters out there.
This is just how I see it though. It would look different if I included the theories I have but I wanted to keep it somewhat grounded into the topic at hand. Until we get a grasp on the gap between lvl 5 superhumans and the Numbered, it seems a bit too early to say anyway. If the gap is as vast as I think it is between the 2 then it doesn't matter what humans and superhumans do, they'll lose in the end.
I think the best scenario we can hope for is that whoever wins in the end at least provide some shelter/protection for the people that didn't want to go superhuman, something in line with that number 1 possibility alkeera mentioned. Even in a chaotic world what the top dog says is law after all, maybe a MC with low corruption and high morality?