I feel like he's had defensive deficiencies his whole career... and goes through patches where he just cannot catch anything.
But he's tall, fast and strong... and I think he takes a lot of yardage hitups... those are the exact physical traits that rorters have looked for in outside backs for a long time now... emphasis being on tall
Tupou, Manu, Latrell, Suaalii, Marky Mark, etc. even Billy Smith is tall.
So from that standpoint Young was a perfect fit for them and was likely being groomed as the Tupou replacement.
Then when they got him into the building, Robbo realised he's dumb as a doorknob and it didn't matter how many physical traits he had he just couldn't coach that level of dumb out of him.