I compare him to Watt as a prospect. Nobody could tell that Watt would turn into an all-time great when he got drafted. Considering the huge amount of talent the 2011 draft held, Watt was viewed as a bad pick by most pundits. Watt is the prime example that you can get by without any bend and somewhat stiff-looking, if you have a good first step, excellent hands and non-stop motor. Zach Allen shares these traits with Watt. Their college film is similar. And no, you can't even expect Allen to turn into 10% the player Watt has become as a pro.
The comparison to Watt isn't meant to put pressure on Allen. It's just that they are quite similar as prospects. If you want a more reasonable comparison, I think of Brett Keisel. Same size, below average athleticism. Played upright, but won with hands and relentless spirit. Never a star, but had a great 10+ year career with the Steelers. Now Allen would already be a success if he turns out to be half the player Keisel was. Keisel was a similar, although much worse prospect than Allen. JJ Nelson compares to DeSean Jackson favorably, but he is a much worse player. They are just very similar. You get my point.