That is an incredibly small sample size. Hard to say that is Chadli at his best and not just a purple patch which many players have.
Not a purple patch, he was (for a long time) the only one of the 7 that wasn't shite (even Eriksen struggled at first). He got better and was on fire under Poch, but then he went all David Bentley after his dad died and never recovered.
I wouldn't say it's a small sample size - his form is entirely comparable to Son (ok first season, picked up second season), except Chadli was consistent up until January - it's the post January Chadli that, unfortunately, everyone seems to having living in their memory.