I think mobius could be released in DL at 3, Raiza would probably be too powerful, and Caius maybe in time.. or as a 1 of. Granmarg is not too good since most set cards will be backrow that is mostly chainable, and zaborg's mandatory effect could hurt you too especially when you use SE.
justification for mobius at 3: tribute summoning in itself is slow, costly and not always guaranteed, being able to destroy 2 spells/traps is very good but again, some could be chainable. And a lot of skills already involve a +1 field spell card, meanwhile any monarch deck would be heavily reliant on skills like restart to not totally brick, even though the last might not be an argument to some...
^except for the fact that raiza is way more versatile, consistent and devastating than red Dragon ninja. Being able to deal with everything on the field and not just set cards, while setting you're opponent back a turn with their draw, with no constraints of having ninja cards in the graveyard, raiza would very much be gamechanging at 3.
the only advantage of red dragon ninja is that the set card cannot be chained. The choice of either putting it on top or on the bottom of the deck isn't really a big advantage since in most cases you want to place it on top of the deck anyway. Raiza IS BETTER than red dragon because for Raiza you do not have to include ninja cards (grave), and it can target face up cards too (unchainable anyway).