Pass catching doesn't happen in a vacuum. I'm not talking about pure 'drops' or how good his hands are (which obviously doesn't change regardless of where he is playing). Most 'catches' in the NFL are contested. 'Contesting' against more athletic, quick CBs is much more difficult than at the TE spot. Now there are some things that may be MORE difficult at the TE spot, like retaining possession during a big hit for example, or having to catch passes over the middle knowing contact is moments away. We don't know how he would fare in those situations. But I think Sims athleticism and relative quickness advantage over LBs and safeties would give him more 'open' receiving opportunities than he is going to experience at WR where the guys covering him are equal or better athletes and have the speed to contest catches. Does that make it clearer?