Looking at stats at face value rarely tells the full story...
I tried to follow his progress as I was pretty excited about him five years ago, like a lot of us on here. To be honest, I thought he was going to fade into obscurity at first. He wasn't a starter at first, which is understandable as a young player in a new league coming off the back of two poor loan spells, but he wasn't overly impressing in the cameos I saw, just the same old frustrating Januzaj with nice touches but no end product. I almost forgot about him until I saw he was starting games near the end of the season and had just scored in a 5-0 win. He was performance in a 3-0 win against Atletico and started all Sociedad's games as they actually finished the season quite strongly with 4 wins in their last 7.
Tldr, stats don't tell the whole story, he started slowly but how else would he have got called up into a Belgium squad packed with attacking talent (and after 4 years without a cap) if he wasn't in good form the last few months?