Lewis is worthless. At least Sidney provides offense. Lewis provides tampons on both ends of the floor. It is amazing to me that people call for him to play more minutes than Sid.
but I've stopped counting the number of times Lewis gets blown away in one-on-one situations against good post players that Sidney contains. Watch with a little objectivity and you'll realize that Lewis is really not that much better on defense. That being said I think Lewis is a valuable part of this team, but only as Sidney's backup, nothing more.