Rimuru should have been boned by the very moment that Low 1-C artifacts and High Hyperversal Range are a thing.
Staff of Magnus = Capable of nullifying all sorts of energies and reality warping. It can destroy the high complex multiverse with its massive, infinite, metaphysical output alone. In TES, many people could not destroy the world because the staff has a limiter. In VS debates, the plot limiter does not apply.
Skeleton Key = Unlock everything. LITERALLY EVERYTHING, even concepts and abstracts. I read Rimuru that he does not have conceptual manipulation or law manipulation, which The Dovahkiin had it by default via Thu'um. The Skeleton Key is way more powerful. Just imagine, The Dovahkiin wants to unlock and steal the Sage, he can just do it. If the Dovahkiin wants to copy Rimuru's abilities, He can just do it. This one is much better, The Dovahkiin can use the Key to create an exact shadow of Rimuru, and this shadow has exact power as Rimuru fighting for Dovahkiin as Nocturnal once did with Sotha Sil (Both Nocturnal and Sotha Sil are Low 1-C gods).
Mehrunes Razor = Change reality through law, abstract, concept, reality manipulation. It is similar to Skeleton Key, but you required to have a certain knowledge about what you want to do. The Razor is so sharp that it can cut through everything, even changing history can be done through "cutting". The Razor is so powerful that it can make one into a Daedric Prince (Mehrunes Dagon was a lowly Daedra becoming a Prince due to a Magna Ge using the Razor), or alter the impossible metaphysic laws of Low 1-C gods (Mankar Camoran cuts through Akatosh to become a Dragonborn).
Spellbreaker = Nullifies all spells and magical attacks. It can do it before one can even think, and shield can read the future along with all possibilities to make sure it can prevent mages casting any spell at all. It is a Low 1-C artifact channeled by the power of Peyrite, Daedric Prince of Pestillence himself.
etc....
Even if Rimuru want to pull a NLF, The Dovahkiin has WAY WAY BIGGER arguments for NLF.