I agree with much of this. I do think Shakir is in the most potential danger of the 3. I don't mind Shakir and hope he does well, but he isn't super big or super fast, so he has to win with quickness and he HAS to have sure hands. He is reportedly struggling with his hands in practice and that drop in the last game was bad. I don't know why Isabella wouldn't have an opportunity to beat him out.
I am not saying that Sherfield or Harty are bad, but they are far from proven (other than on special teams). Now, if people want to ascribe Harty and Sherfield's lack of stats to lack of opportunity- couldn't that also be said of the other guys trying to win spots? I fully expect Sherfield and Harty to make the team, I'm just saying that they aren't truly established NFL receivers that should be locks.