Most consistent dps class throughout ffxiv lifespan. Planning on switching mains.

[MistakeNot]

I want a class the stays consistently good or average and never roller coaster.

Then you should avoid MMOs altogether.
All classes get tweaked with each expansion, so which ones are on top will change.

But don't worry too much about which class is supposed to be "best" or "worst" - they are all viable, and player skill matters more than which class you chose.