I can't believe how little defense is valued on this site.
If IT went to the Spurs, Cavs, Wizards, Rockets, OKC, or Golden State, and others, he'd come off the bench. There is no way those teams put up with the team having to cover-up his lack of defensive value, to watch him just score. And pay him max, lol.
If we're lucky enough to get a Hayward, Fultz or Griffin you realize the number of shots IT takes will decrease, along with his scoring average, and he'll be expected to facilitate, and gulp...defend.
The second part of what you said is obvious and uninformative. Steph Curry scored less this year with Durant on his team, and his role changed. Ray Allen scored less and was "expected to defend" when he came to the Celtics. So? Gordon Hayward would get much better shot opportunities with IT on the floor rather than, say, Marcus Smart. And yes, IT might be able to do more on defense. How do you know that wouldn't be the best lineup we could field?
And there's no basis in fact for the first part of what you said. It's just your opinion, which is fine. but you can't say for sure you know whether those teams would start him. Other championship contenders have started really bad defenders before because they were good offensively. IT might be a worse defender than many of those players, but he's also a much better offensive player. He just made second team All-NBA, and you're 100% positive that any other really good team in the league would bench him? I can't think of any historical parallel for that situation.
But none of that really says much at all about the question posed in this thread, which is whether it's a good idea to trade IT for Kemba Walker. If you want IT gone, fine, but you can do a heck of a lot better than Kemba Walker and a late lottery pick. Send him out WITH a pick to get a much better player (like Butler), for example.