Watt is the best defender I've ever seen, period. He crushes the middle, draws double teams, and still pass rushes better than the best edge rushers. His 8 forced fumbles are on pace to match or exceed both LT and Reggie White over his career. The guy already has as many TDs either of them and will probably double LT's recovered fumbles. Then his outrageous 30 passes defended borders on being ridiculous. Each pass knocked away is almost as good as a sack.
If he doesn't get injured he will probably surpass Deion, Lott, Reggie, then LT as defensive GOAT. He's that good.
That said, you can't fault Dallas for taking Smith, who has become an elite LT and will be the cornerstone of this offense for years.