Fair enough, don't think he's really suited to being a defensive player.
It's difficult to tell though, because obviously we don't get the sort of data about rugby players athleticism that we do from NFL prospects/combines.
Just found this video of George North doing 40m in 4.97 whilst in the scarlets academy, converted to a 40YD time that's 4.54... which is quick.
Someone will probably tell me that you can't accurately transfer a 40m time into a 40y time, but I can't see why not - it's 3~ yards difference.
If we assume that GN is probably slower now, than he was then, due to being bigger... and that Watson is appreciably faster than GN - I think AW could run a sub 4.5 40YD.
That would put him in the ball-park for WR's and Corners.