One thing with Iman is he's just 25 still. Conceivable that he has some growth in his game left, or at least refine what he has going now. And like Ben, he's never really had a chance at being a 30+ MPG guy and always been stuck behind someone.
Like WCS, he's also a guy where you have to ignore individual box score stats. Here are a few stand-out numbers:
6th in DRPM among SG's,
13th among all guards
Cavs Opponent ORTG:
ON-- 100.8
Off- 104.3
44% Opponent FG when defending. Normally 44.7%
Now some of these are likely inflated because Cleveland is an excellent defensive team, but when just about every metric is telling you a guy is a good defender... he's a good defender. Also matches up with the eye-test that he's very good on that side of the ball.
And how good of a shooter Ben is compared to Shumpert almost doesn't matter at this point. Ben is completely a lost cog in our offense and is making 0.9 3s/game this season.... We can certainly argue (and I'd agree with) that we've severely underutilized him, but he's easily the most replaceable player on offense because he's a ghost out there. Not a playmaker, low USG, doesn't crash the glass etc.
We're also at the point now where you have to think long-term with Ben. What's he going to show with us in the next year and a half that we haven't seen in the past 2 and a half seasons? Are we going to commit to him at 5-6 mil a season or lose yet another asset for nothing? I've wanted it to click, but we're at 178 starts+ 5800 minutes now and we're still at the point of hoping he'll "get it."
Iman's not the perfect piece at the 2-guard and I cringe at the prospect of him and Rondo floor spacing together, but he'll make a significant improvement to the worst guard defense in the NBA, he's still just 25, has playoff/big game experience, and is locked into a reasonable deal long-term. We can't complain about having an atrocious defense and then scoff at a guy who would improve it for a reasonable cost.