I think you guys are overrating his liability on defense. I haven't watched much of him this year but it seems to me like the lack of defense is based on rep, but the stats tell a different story. According to Synergy, he's giving up .77 points per play, good for 79th in the NBA. According to 82games, he's split his time between PG and SG and has defended 1s to a PER of 12.6 and 2s to a PER of 14.3, both impressive stats. Last year, he defended 2s to a 13 PER.
Now, these stats aren't perfect. Both the Hawks and Blazers were 5 points better on defense with him off the court, and he does have a rep as a below-average defender.
I'm just saying that maybe his defense isn't as big a deal as some people are saying, and that it's worth the minor lumps for his offensive production off the bench.