He was drafted as a wide out and his lack of top end speed is an issue when slotting him at that position. Instead, if you think of him as a tight end, his combine numbers become elite for all categories with the third fastest 40, second highest vertical and the most bench press reps. His height and weight put him at an apparent disadvantage compared to other TE in the draft, but his upper body strength is so superior to the average tight end that his 228# might not be an issue. Even compared to OL, only 12 (out of 37) benched more reps than he did at the combine. That kind of UB strength would allow him to neutralize many DL/edge rushers and LB on run plays.
His top-end speed isn't that bad - he ran a 4.53, same as Mike Evans and in the same ballpark as top receivers JuJu Smith-Schuster (4.54), Davante Adams (4.56), Nuke Hopkins (4.57), and Michael Thomas (4.57). He falls in the category of most NFL receivers, where he isn't going to win with his speed, but his speed can't be ignored.
I don't think it makes much sense to move him to tight end, as you seem to be suggesting, but I think you hit on something about his physical profile. Gronk was a tight end with tight end athleticism who was almost built like an offensive tackle; he was a physical mismatch for linebackers, much less the defensive backs who often covered him. In a similar way, Harry, is a wide receiver with wide receiver athleticism who is built almost like a small tight end. He's a physical mismatch for the cornerbacks who are going to be covering him, especially if they use him in the slot and he gets matched up on smaller slot CB. He's not going to outrace those guys, but he is so much bigger and more physical than the players who will be defending him, he will still be a handful.