It may seem that way but that's not the case at all.
Nerlens Noel is a very good defensive player. He was top 10 in both steals and blocks as well as other analytical defensive stats. Okafor showed off his nice offensive game by scoring 17 a game on 50% shooting. Both are 6-11 with complementary skills sets. Now add a guy like Ben Simmons who can possibly set them up for easy baskets with his playmaking/dribble penetration skills.
Let's not forget that if Joel Embiid ever comes back and plays half decent, that's a lot of size to contend with.