Understand the fact that he is only 23 years old and we can't say that his weakness against spin will always remain. He can get better with it as he gathers more experience & team already has few guys like SKY, Tilak, Ishan & Nehal who can play spin well. If they have to replace him in spin conditions, they have Brevis & Stubbs. Both are good players of spin.
He was never a frontline bowler and will only come to chip in few overs and he did even pick up 6 wickets this season, economy may be close to 10 and can't complain since everyone in MI was leaking runs..