All the gods are cats compared to the tiger that is Heaven. Why is Heaven scared and jealous of us then? Because their must be SOME kind of hidden mechanism in COP that neither TW not Wu Heir discovered that is causing the Heavens to be envious.
You are overthinking it too much even heavens can't kill gods and had to scheme so much and also had other folks helping in that scheme to even put a god in weakened state and that god himself was trying things deliberately which would make himself vulnerable if tang wei wasn't trying to do that heavens wouldn't be able to do anything and let's not forget butterfly f*cking him over it took so much to do all that even then he wouldn't die that's why Heavens likely wanted SLM to destroy poma World so stuck 1 hp tang wei can be killed and even there it needed schemes to get SLM to work.
The heavens hate COP because it is the fastest route to godhood and if they aren't harmed and get the right help you get a guaranteed God the heavens doesn't want a God not even 1 since heavens cannot kill them each God while nit as strong as SLM still can escape from her without harm and combined and can put her to sleep that's how human Gods are still at the top.
Heavens already has an issue with humans in general since their fate is in their own hands and COP just makes it all easier other species unlike human have built in limits while humans don't .So the beasts who reach godhood are allowed by heavens while the humans cannot be stopped they reach the peak on their own it's why heavens have a hate boner for humans and COP as I said is the prime example of it so the biggest hate boner.
Also heavens isn't one proper entity it contradicts and f*cks over itself a lot too according to niki and gets mad over it Schizo a*s heavens in poma lol.
But yeah godhood is the peak for a reason even to Kill one they need to do so much and this is when one tries fighting a god can always escape poma gods have great defense.
So yeah heavens issue is that no one should reach godhood and COP makes it a sure deal if they aren't harmed.
SLM is used a proxy for a reason since heavens cannot do much to gods and even SLM herself cannot if gods didn't care about other planets getting destroyed since niki said every single god can easily escape .
Also as you said if niki removed any concrete rules from the book you will be disappointed so you see it isn't about COP being limited or anything the verse itself has a final stage and that's godhood that is the BIGGEST rule even more strict than the one of Ruo since Ruo's rule is not even concrete it is something that is done by heavens and maintained by it while godhood as a stage isn't heavens doing it is the peak of the verse made by niki . There isn't anything after it and that is the real rule independent of whatever heavens tries as godhood has nothing to do with heavens as the gods are already out of heaven's grasp.
So the hardset Rule about the verse is godhood for a reason same reason why all gods are still relative in power even though someone like dream weaver should be nothing he is basically opposite of COP in potential and yet the final stage is the same he was able to reach the apex it's niki's way of showing talent isn't the only thing.COP basically makes it all easy and will also allow the person to create a lot but power wise the gods all stay relative even if Sovergien is slightly stronger.
So again Heavens doesn't want anyone reaching godhood and COP makes it a sure deal so that's why the hate and trying to f*ck them over.
Also if niki wanted to break all the rules for this mc wouldn't he want to right that and show it like how there is actually anything beyond godhood even though there isn't but still if he wanted to write he could have with this mc since he is the author but there is a reason he doesn't even wanna write past NS wu heir will reach godhood his throw away line and then be done with it and how he has been trying to show it each time how gos are relative in power even though the huge talent difference among many of them niki has made it clear time after time COP is what makes reaching that place(godhood) easy.Gods are out of heaven's grasp while SLM even being supercharged by heavens and being stronger still cannot kill one nor can she trap one as they all can escape.
Anyways I doubt WU heir even reaches godhood whatever new story will be in nikiverse i doubt it will show what Wu heir or Maybe niki might throw us a bone and in one of the epilogues show WU heir reached godhood.
Also you deffo are Wu heir's strongest Soldier ever(Compliment).