Well, no, you're a loveable loremonger! I mean, much like a fishmonger, you can't catch all of the fish in your net/sell of all them at your stall. Some Lore will be left unexplored by even the best loremonger, because they don't necessarily use every type of net...
*Musters my best Emperor Palpatine dialogue in the second Death Star throne room impression*
I'm afraid though, Moose, that Hildibrand is quite canonical. You see... the Blue Magic spell #35 is the spell, "Missile." Though it is said to be, ,"A magical imitation of a warmachina technology..." it is only learnable from Enkidu for the Warrior of Light aka Azuro the Second. Blue Magic is canon, because the Whalaqee are canon as is the New World.
Combine this with the fact that after we beat Gilgamesh in the Battle of the Big Keep, he takes on the mantle of Yojimbo in the Far East. This is unknown to us until the Stormblood events leading up to Kugane Ohashi, but it is true, nonetheless. The events of Kugane Castle are canon, are they not, as they exist outside of the comedy bubble entirely. In order for him to be driven there, he has to be beaten in the 2.5 Hildibrand line (though it is true you can unlock Kugane Castle without doing Hildibrand, but time bubble shenanigans).
But wait, there's more!
Consider Inspector Briardien. He is introduced under the auspices of the Hildibrand questline, but he's given his own, very real, splinter cell wherein he recognizes you from the Hildibrand questline. The Scholasticate questline in Ishgard! In the course of this, he makes mention of the Sil'dih sister he's in love with imprisoned at the end of ARR Hildibrand.
Anyway... *waves my hands too for Enkidu* Enkidu is most similar in summoning to Thordan, as I'm taking it, Thordan VII Ye Olde Pope, summoned him, himself, right? I mean, he used the faith of every Ishgardian, and drew the Primal into his own being, so they don't share that aspect... but it would seem that any individual given enough resources can perform a summoning if they know the means. Tsukuyomi also follows this trend(Shiva too), though obviously what sets Enkidu apart is that Gilgamesh summoned her accidentally!
Now that I think about it... Odin is wildly similar to Tsukuyomi as well, given that all that needs happen is someone takes up Zantetsuken. Could it be that one of the weapons Gilgamesh has collected over the years allows him to summon primals by his lonesome, or is he some sort of flamboyant, itinerant ancient unsundered due to always being on the go, mostly via The Rift? We may never know, but I could speculate all day. I'm a speculationmonger!