Just like all Deadra aren't the same race, I don't think all deadric armors are made of the same materials. Iron and silver armors could both be considered by deadra to be "Mortal Armor".
Is it ever suggested in the Knights of the Nine quest the the Hero of Kvatch is a reincarnation of Pelinal? Because I don't think it is. Why can't the HoC just be some random dude that beat Umaril?
The only other person that is close to spelling out the Divine Crusader II might be Pelinal Reborn / Mantler is the Prophet. And some would say the Prophet might be another Talos aspect, namely Zurin Arctus because of the Divine Blessing. That Snarker literally said the word we are the embodiment of the Crusader.
Though, others say the Prophet is just... some dude, who vanishes when the Event has been done. Like any Prophets when their job is done. He might be a Priest of Talos with a strong connection to his Divine, hence would explain why he was able to give such a strong blessing to us since he is a powerful conduit for Talos to give his blessing through.
But no... there's nothing wrong in the story of some random dude beating Umaril. We're not talking about the personal playthrough, or our own canon. We're talking about ES canon, WHICH if I remind you, is to be taken with a grain of salt or as full blast cannon. Your choice. That is how Elder Scrolls have always been, a bunch of lore which we can choose to say it's relevant or not to our playthrough.
We're talking about who the CoC is (who they could be) and lores that would be relevant to our tale, not some random dude. Oblivion received a lot of flak that was unnecessary due to the fact CoC is irrelevant, that we weren't the hero of the story. The game never ever, and will never tell you you're the MacGuffin, friend, unlike the Dragonborn's or the Nerevarine's story. Instead, you're stressed as the important MacGuffin's Lancer. The reason the Hero of Kvatch is being pointed out as Pelinal of some form is because our tale (Main Quest) has extreme similarity to what Alessia and her Co faced.
It adds some romanticism to the story of Oblivion, some relevance to it. Some well thought out depths even though it might be coincidental.
That's my argument to Oblivion story being close to Alessia's, and therefore reinforcing a strong theme behind CoC, Pelinal, our walk with madness. Why not make Oblivion's story better because of this? Adding the irony of the tale of the First, Alessia and Pelinal being mirrored at the end of the Dragonborn Empire with the Last, Martin and us.
KoTN was just an official stamp on CoC, not the beginning of CoC's walk as Pelinal v.2. BUT there's nothing wrong in saying, Well... that's not MY CoC. Which is good, lores like these aren't set in stone. But there is no denying the lores behind our Hero of Kvatch here. You can make use of it or ignore it.