This question is quite similar to my Regigigas question before. Since Archeops' ability is Defeatist it is currently in the PU tier (like Regigigas because Slow Start). I actually wonder what tier Archeops would rise to (if it even did) if it had the option to have a normal common ability such as Pressure or Inner Focus or something. For those who forgot the tiers, here is the list of them:
When leaving an answer, I would like to know why you think it would be here.
Check out Archeops and it's ability Defeatist.
Archeops Smogon analysis