Many great comments were already made, so I'll keep mine short and summarize my thoughts. Bug/Psychic typing already gives many commong weaknesses, and this means almost every scarfed revenge killer will be able to revenge with the appropriate move. Just to cite some notable examples, all scarfed Landorus, Terrakion, Genesect to an extent, Tyranitar, and many others will be able to easily revenge. Now, about defensive (or just slower) checks/counters, Steel types, and in particular Heatran and Skarmory seem particularly hard to overcome; a Fire coverage move would let Heatran wall it comfortably, while a Bug/Psychic/Ground or Fighting coverage is easily handled by Skarmory.
In my opinion, we should give CAP4 adequate coverage moves to threaten every check/counter it may have, but it would need to use all its moveslots to do so. For example, a Bug/Psychic/Ground/Electric coverage handles basically everything bar revenge killers/priority. The user must then choose between running a set-up move like Quiver Dance (and thus being walled by something, losing one coverage move), or to go all-out offensive (threatening basically every switch in, but being much more susceptible to faster threats). Both choices are very risky, since a set-up set is still quite susceptible to strong priorities and very fast scarfers, while an all-out offensive set will be worn down fast while switching around (weakness to hazards), by its eventual Life Orb, and is likely to be eventually killed by something faster.
So, to sum up, depending by the set, CAP4 should have many different checks, but no absolute counter. Heatran and Skarmory will be natural candidates to a full counter if CAP4 decides to use only three attacking moves, while faster pokes with a SE move will easily check any version that is unable to set up.