I don't think he was, most people knew he didn't have the raw talent to be as good a player as Witsel for instance
He's solid player but he couldn't make it at Porto, he came back to Anderlecht but he never fitted in (and while playing at Standard he on multiple occasions said he hated Anderlecht), the fans were 50/50 on him, he was injured a lot, suspended a lot and frankly he was getting in the way of Tielemans' progression
And now with Burnley he's only played in like half of their games so I don't know. I wouldn't call him a bust but yeah, I think most of us thought he would have gotten more out of his career than what we've seen so far.