DECs have pros and cons. Pro, they are sitting left seat with a flow now and have a large sign on bonus. Cons, they are sitting left seat with FO's that are more senior to them, perhaps perpetually knocking them down the list.

You have to keep in mind that every FO hired before you got here is a potential issue. If you are OK with that and the money makes it worth it, do it. If you live in base you are golden.

As for time on rev, I would put it 1.5-2 years, as that is the average upgrade time for FO's that were hired in the late 2016 early 2017 hiring spree. Once they are out of your way you can start to get off RSV, however you may not want to if you live in base.