Didnt he play half a season before he got here? He was probably gassed by the time summer came around. I have high hopes for him in year two after a proper offseason. Id hate to see him go.
There's a few things to consider, this is a big one. Another is that Armas intentionally moved Kaku further from goal and the middle of the field where he was more likely to get on the scoresheet. Franco Panizo did a write-up on it for SBI back in September. Kaku himself also said that opponents started to focus him more individually as the year went on, something that will happen to every #10 we sign until we get more dangerous guys around him.
And most importantly, something I don't see anyone talking about - even though Kaku's personal numbers went down under Armas the team's attack as a whole got better. I think its unfair to say that Kaku suddenly had nothing to do with that. Playing from deeper and wider spots, he wasn't often the one playing the final pass but I think his distribution was still a huge part of the successful Supporter's Shield run.