I think the issue here is not whether Iamtdg thinks Will Fuller should be a later round pick, I think everyone respects his right to value Fuller however he wants.
But similarly just because I would say "No, I wouldn't take Morris Claiborne in the first round because CBs suck!!!" it also would be incorrect of me to label Claiborne a target for our second round pick. Because there's a 0% chance that someone else doesn't take him high.
Iamtdg may think Fuller is a 4th rounder or whatever but he's not a sleeper and he's going to end up going at worst in the third round, I'd bet. That is consensus at the moment so it's not really correct to say he is a sleeper since most sources have him going early, and a sleeper is by definition someone who will have success after going late.
In fact Iamtdg doesn't seem to think Fuller will have any success at all, so he can't be a sleeper no matter where he is taken, then, since he will never pan out according to Iamtdg's projection.