1. Momoshiki doesn't have a kekkai mora or at least the manga never said so.
2. Nagato used Madara's eyes to create those pain powers, doesn't matter if Madara is the original owner or not.
3. With that logic, Nagato should be able to use Limbo Hengoku too.
About #3: Nope, Nagato not being able to use limbo is akin to how Kakashi couldn't deactivate sharingan. In both cases they couldn't be done because the users in question were not the original owner. Also, you never responded to my post about the writing perspective. Here it was:
Your premise doesn't make sense from a writing perspective though.
Why would Madara's and Sasuke's absorption just be some generic absorption when there was already an established rinnegan technique (preta) that served the same purpose by the time Madara debuted and by the time Sasuke awakened the rinnegan? Like do you actually think that when Kishi drew the scene of Madara absorbing Onoki's jinton that Kishi thought in his mind "hmm... I better make this absorption weaker than Preta path for no reason whatsoever"?
If not Deva, then what do you call Madara bringing down that meteor?
Finally, why would Kishi give Madara and Sasuke practically useless rinnegan eyes with almost no real offensive ability? That is what leaves the worst taste in my mouth when it comes to your belief about Nagato being the only one that can use Deva, Preta, etc...
If you are to be taken as correct then Madara and Sasuke's rinnegan eyes might as well be contact lenses when it comes to battle power, because they are near useless by your logic.
Let's look at your description of Sasuke's paths for example:
1. Bijuu vessel susanoo
Ok, so you're telling me that one of Sasuke's "six paths" can't even be used outside of the rare case when the bijuus are around? BS, but ok... Let's move on
2. Indra's arrow
That requires the bijuu perfect susanoo, so this has the same flaw as above! He'd be better off just using chidori related techniques. Heck, he already showed that he could use chidori with susanoo before he absorbed the bijuus. Great so now 2/6 of his paths are rendered a flop. Keep in mind that this is already a third of them.
3. Dimensional Portal: Cool for travel or for investigating other dimensions, but has almost zero battle application. That's 3/6 down.
4. Amenotejikara: Not really an offensive technique by nature, but could be dangerous if used strategically or for blitzing.
5. Chibaku tensei
6. Absorption (apparently less than preta for whatever reason)
So you are basically saying that Kishi basically only gave Sasuke two offensive techniques (that can't really be spammed) as his rinnegan techniques, and he made half of his arsenal a flop that can rarely be used? He did arguably even worse to Madara. Yet he gave a borrowed rinnegan user 6 actually useful techniques for battle?
BS!