Eminger was the 25 year old former first rounder. The Flyers obviously valued him higher than they should have (even though Washington did throw in a 3rd round pick, it wasn't straight up), but it's completely understandable that they would value him over Erskine. Erskine was three years older and was basically a journeyman enforcer up until that point. He had spent some time in the AHL in every season prior to that one, and even in 2007-08 he wasn't an every game player (he only played 51 games).
Agreed, I think he was a little underrated partially cause he didn't go the NCAA route an an American and partially cause he played for a Hunter team(system-system-system). If anyone had known Carlson was this guy he would have gone top 10 easily. Perhaps top 5 depends on your preferences. Absolutely loaded class for defenders and he got overlooked.
He'd probably go Top 10 if you redrafted today, but I wouldn't guarantee it. Karlsson, Doughty, Stamkos, and Pietrangelo are the obvious top 4 in the draft. After that there's a group of Carlson, Josi, Myers, Hamonic, Brodie, Atkinson, Stepan, Eberle, and Holtby that could go in almost any order. And if you're purely basing it off hockey skill, you could consider Voynov in there as well. Depending on your preferences, it's entirely possible he could slip to 12 or 13. That draft was loaded with defensemen.