Odin's HGR seems to regen on the level of type 3 or 2 concept erasure only, while Uriel's is type 1
The concept magics in Fortissimo works different than your usual Concept Manips
It's not depending on types, it's depending on the AP of the concept that is trying to overwrites the Concept Magic.
"Concept magic can only be overwritten by a stronger concept"
This is universally how the Concept Magics in Fortissimo works. At first, I also thought it's layered thing, but then after I rewatching some of the Concept Magic duels, it's turn out that whichever concepts got more energy win.
That is why when 2 concept magics clash,
it's turn into a DBZ style of clash.
You have to defeat the concept magics with concepts that have higher AP, otherwise the Concept Magic will overwrites it with it's own concept.
And Odin's 3-C tier is just him holding back (hence why the key is called 50% power. His 100% is Low 2-C for being the strongest magi ever live, which would put him aboves the post-ragnarok magi like
Reiji ) and it's implied that Odin cannot overwrites Das Rheingold even with Gotterdammerung at 100% power.
Uriel's highest tier is 3-B, or perhap he is also holding back like Odin ? If he can pour more AP into his concept manip (more than Low 2-C) then I'm fine with him defeats Odin.
EDIT: wait, come to think about it, I cant argues low 2-C Odin since it's not in the profile (and considering the inconsistency between Fortissimo and it's sequel, Kadenz Fermata). Welp, Uriel can take Odin's place then.