Originally posted by The Ellimist
1. Neither Bilbo nor Frodo could use the ring properly
2. The ring doesn't have Sauron's full powerGranted, these two points might also apply here, but it's a matter of degree. In the case of LotR it's probably something like:
Sauron (sans ring): 30
The One Ring: 70
Full Power Sauron: 100
The One Ring (that Frodo can harness): 7
Frodo: 1
I think we're on the same page for the most part, then. So, going off of the two points you brought up, the pertinent questions are, "can Frodo Celeste use the ring talisman as well as Muur" and "does the ring talisman have all of Sauron's Muur's power?"
Exactly how much power was vested in the talisman is for all intents and purposes unknowable, so I won't comment on it. I don't find it to be particularly relevant to the question of who is stronger between Celeste-Muur and Muur, besides (as both were in possession of the talisman). With regards to whether or not Celeste could make full use of the talisman's power, you're right to say that we can't really know that for sure either, since the talisman has never been in anyone else's possession on-screen for any significant amount of time. What we do know, however, is that (spirit) Muur cannot use the force by himself; he requires a living, force-sensitive host to do so. Furthermore, it stands to reason that the breadth of his powers will increase as his host becomes more powerful, which is one reason why he seeks superior partners like Krayt and Vader.
So, with that in mind, which do you think was the better vessel for the talisman's power? A, the body of Muur, the man himself, and one of the most prominent Sith Lords of his day? Or B, the body of Celeste, who was just one of the dozens of Jedi agents working under Lucien Draay, and who actively resisted the talisman's influence? I, myself, have my doubts about option B. That's not to say that it's impossible; on the contrary, it's fairly widely believed that Exar Kun was stronger when channeling his powers through Kyp than he was in life, but that's because Kyp himself was exceptionally powerful. I haven't seen anything that makes me think the same is true of Celeste.