I'm going to dispute a few things there. Darcy is 3cm shorter than English but the same height as Grundy who is supposed to be the best ruckman. The point being, height doesn't mean you're going to win the hit out, especially at boundary throw ins where it's more of a wrestle for the correct position.
When comparing Darcy and English, I reckon Darcy comes out on top stats wise. Both have played 18 games so far but Darcy played 8 of those when he was 18 and 8 more when he was 19 (and one of those he didn't record a stat as he was injured in the first few minutes). English has played 9 of his games this year and turns 22 in a month. As a result, you would think English would be far ahead of Darcy stats wise. You'd be wrong.
Darcy averaged 12.3 possessions in his first year and that has since come down to 10 but I'd wager a fair part of that is due to playing alongside Sandi in his second year (and recording no stats in 1 game) and then Lobb in his two games this season. English has had free rain to take the main ruck mantle at the Dogs with few other ruckmen in the squad and while his season has been promising, it's no where near what Darcy has produced on occasion.
Just look at hitouts where the 3cm shorter Darcy averages 31.6 (again, with a 0 amongst his 18 games) while English sits at a paltry 15.1. That's reasonably pathetic ruckwork so you'd want to be getting the ball a lot more around the ground which as per the last paragraph, also isn't happening. When you take into account the fact Darcy was reasonably unfit in those first 2 years as he tried to lose weight, I think there's a hell of a lot more potential in him to expand on those disposal figures than English who has always been touted as a runner.
So yeah, Darcy measures up quite well and I'll be interested to see how he goes in the second half of the year coming back from a foot injury (that probably hasn't helped his fitness and has him somewhat underdone for movement around the ground).