Well, that's not entirely true.

The Nords brought their pantheon to Tamriel and it includes spirits such as Kyne who are virtually identical to the modern Divines. Was this due to the influence of the elves of Altmora? Who knows.

Meanwhile, the Altmer worship some gods such as Xarxes and Phyngaster who do not appear to be Aedra, just Aldmeri ancestors of great renown. So the Nine Divines are probably a synthesis of Ayleid (not the Daedra worshipers you thought they were), Nordic and Cyrodic deities.

And since elven and human religions are in actuality just memories of the Dawn Era, their beliefs are equally venerable. The 1st PGE may call the elves the Elder Races, but this doesn't mean the same thing it does in LotR since they're no older than humans. Older recorded history and complex civilization, maybe.

Yes, the eight divines are a synthesis of the different culture's gods. As I recall though, many of these gods were directly taken from the elven pantheon, and weren't present in human ones.

Also, about the ayleids: didn't they worship the deadra? I don't know that much about ayleids. Either way, I can easily be wrong about some of this stuff. This lore is very complex and abstract. It's always fun and interesting to discuss this stuff with others though.

It seems that Cyrodiil's human population worshiped the Ayleid pantheon. It would be fascinating to read about their own religious beliefs, and if they worshiped an embryonic Akatosh (a pro-Nirn one) in some form. Presumably they didn't worship Lorkhan, as the Song of Pelinal depicts Alessia having a revelation concerning him, where she invents the word for freedom.

There is definitely lore accusing the Ayleids of being filthy daedra-lovers. And Umaril for his part, was.

But I think we're supposed to take it as mostly sensational human scholarship. Oblivion's Ayleid ruins have statues to Auriel prominently displayed, the Ayleid worldview differs little from the Altmer, and after all, if they didn't worship the Aedra, Alessia's pantheon couldn't have been a synthesis.

I believe their relationship to the Aedra was more of a contractual, with the exception of White-Gold and its ruler Umaril. That's why the Amulet of Kings and the Tower are so central to the daedra's access to Nirn.

Let me do some research on them. I don't think most people can worship or be allied with both aedra and daedra. Give me a second.

Yeah, they were daedra worshippers. "Devout" one apperently, and even attempted to gain their power, blessings, and even military aid

That'd be Umaril. But the Ayleids were fairly diverse, as the Nu-Mantia Intercept and Last King of the Ayleids (I think) point out.

Everything I've read implies they all only worshipped daedra, not just Umaril.
Edit: There were likely exceptions though, but as a rule they were daedra worshippers.

I don't think mentioning the sensational and unusual aspect of their culture implies anything besides it existed. It's just what interests scholars and historians. And Oblivion's MQ requires that it be emphasized.

But there aren't any statues of Daedra in Ayleid ruins, just Auriel. And Alessia used their Aedric pantheon to create the Nine Divines. I believe you can find a source describing how the Ayleids spread their Aedric faith to their slaves.

Like I said, they aren't my specialty. If you
could find a source that talks about their aedric faith, I'd appreciate it. I can go back to that link involving them worshipping daedra primarily if you want
Edit: there's also the fact that it explicitly states that the daedra are what gave the ayleids an edge over the humans, and helped build their civilization as a whole

Just read all of Shezarr and the Divines. It's short and extremely important. Pretty clearly states that the Ayleids worshiped the Aldmeri pantheon to a great extent.

Amulet of Kings refers to the Daedra Lords as the "patrons" of the Ayleids, so I think I have support in saying that the relationship was highly varied. There's no real reason why you can't worship your ancestor Aedra and pay tribute to Oblivion for some extra goodies at the same time. The puritanical dichotomy of the Vigilant of Stendarr with holy Aedra vs wicked Daedra is a modern phenomenon.

Well the first part of what you said holds up, but there has always been a split between aedra and daedra. It's not a modern thing. Look at the chimer

I think I found a way for it to make sense. You know how many mages use daedric magic, like summoning daedra, but still worship the nine? Maybe it was similar in ayleid days but to a greater extent. Even though they worshipped aedra in theory, they still went against them by working with daedra. Stuff like that happens in real life all the time haha. Makes sense actually.

By fire be purged, filthy xeno scum.

J'ixui has no moral opinion on the conflicts. He just wishes both man and mer could live as one again.

My guy worships a fork he found. He's been hitting the skooma too much I think...