Today's game it's all about the pass and finding as many mismatches as possible. These new aged TE's are basically oversized receivers that forces teams to put corners on them, which opens up the rest of the offense. Yes, you could add a high level receiver to accomplish the same goals. Look at the SB teams, they both had elite TE's. I view TE like having a great Free Safety, not many elite ones, but when you got one, big advantage.
As for Ferguson, think his ceiling is a more balanced Shultz as he can actually block inline. As for a receiver, still needs some development, but he looks better at this stage then did Shultz. Would like to add a veteran to the group if Shultz does depart. However, think one of these top 5 TE's could drasticially upgrade the position rather then just replace Shultz prior production. We saw TO/Witten tandem work real well.