Thinking about this logically, it seems to me that the issue is McDaniel. First, when hired, he was described as a run game guru. However, far too often he went away from the run game when it was working, and too many times he threw the ball on 3rd or 4th and short when he should have run it. It seems that when he saw the big plays made by Tua throwing to Hill and Waddle, he decided that was going to be the basis for his offense. And, there were many times that Hill was covered, but Tua threw the ball to him anyway, even if other guys were open. IOW, McDaniel's playcalling was based on what he wanted to do, and not on what would be the logical thing to do depending on the defense.
I don't think that McDaniel is focusing on small speedy WRs for the sake of Tua, I think he's doing it because he is so enamored with the idea of the big play that he neglects other "regular" aspects of an effective offense. IMO this is why they do well against bad teams and rack up the stats but lose to the good teams who can easily neuter this style of offense. And, before McDaniel, Tua was spreading the ball around more, and not just focusing on one or two WRs. Taller guys like Parker and Gesicki made a lot of big plays and nice catches when targeted by Tua. Even though they were far from being elite, the offense took advantage of their strengths and made them look like Pro Bowlers.
Enter McDaniel, and he rarely used Gesicki as a receiving weapon, but instead wanted him to block the majority of the time he was on the field. Why would you not take advantage of what Gesicki could do well? This is why IMO McDaniel needs to let someone else call the plays; he does what he likes and not what is best for the offense. Calling a fade in the back corner of the End Zone to a tiny WR, or a pass behind the LOS on 3rd or 4th and short to a receiver who has defenders about to crush him, are not logical playcalls.