You must frequent some odd tier lists.
It's not favoritism if both characters being compared get it or something roughly equivalent. Pretending you're not going to use stat-boosting items or scrolls is just lol.
And yeah, scrolls aren't used up.
If Sety is being penalized in the current list for preventing you from getting Cyas, it sure doesn't look like it. Having everyone else lose 6 Hit and Avoid in order to get a single unit as good as Sety is overall a good trade, but I don't think he would deserve High Tier anymore with that factored in. That kind of thing is a silly way of viewing it though, since it's harming both of their tier positions for no good reason. Just rank them each on their own merits. In which case Cyas would probably need to go up a tier, because A Staves and +9 Hit/Avoid to everyone is not Low Tier material.
And I second (Or was it third? Whatever.) the call for alternate route characters being included.