Are you kidding? You have to have a DT who is capable of rushing the passer or the QB will simply step up into the pocket everytime. You reference the Jaguars; Stroud is a monster at collapsing the pocket, and they are actually getting rid of the guy anyway. Thomas is good against the run, but hes slow, and doesn't have the moves to be an effective pass rush. Hes also old as dirt. DT's don't have to be huge to be effective at the position. Ellis nor Dorsey are monsters, yet both are considered the top DT prospects this year. Ellis is only 295 pounds. The trend is more and more towards atheletic DT's who can get around a Center or Guard instead of just locking up with him. Not to mention Young is 6;2" and 300 pounds. He isn't undersized.
And your comment about tackles for a DT being a bad thing is totally untrue. All the top DT's average 40-60 tackles a year. Thomas had 50 this year, John Henderson 40, Pat Williams 62, Kevin Williams 38, Fred Robbins 42, Corey Williams 35 in 9 games started, I could keep going.
You need one big body, and one good pass rushing DT. Young gives us that ability.