I've only been once so I can't compare it to other seasons. But I went in August to Malpelo and Cocos. Malpelo was a miss, with respect to sharks. Aside from a couple of close encounters with some Galapagos that was it. There was so little action we even left early for Cocos. But still...what a place to dive.
As for Cocos, everything was there in abundance, except no whale sharks. However, the week before they had seen 6 in one trip, including one that hung around the boat for a couple of hours. Still, Alcyon was hot with seemingless limitless schools of hammerheads, schools of large tuna were hunting around us on the safety stops, silkies on every blue water drift, etc. The usual superlative diving.