Got a question about wargear.

I am building an isengard warband for the sbg and i see that lurtz has a defense of 5 and his given wargear is armour, shield, and an orc bow.

My question is since his starting wargear has a shield, is his defense a 5 or a 6? I am asking if it should be higher because if i notice that if i take a standard uruk hai warrior for 9 pts, spend another 1pt on a shield, the standard uruk hai warrior Will now have a defense value of 6. This means that the warrior could have a higher defense value than lurtz, the leader of the warrior's warband

It's a 5. He has a bow, so can't benefit from the shield's +1D (check the war gear section of the rules). However, he can still "shield" with it.

As for the Uruk having higher D, that is because he has both heavy armour, and a shield that counts. The heavy-armoured Uruks aren't scouts, and really aren't meant to be led by the scout leaders (Lurtz, Ugluk, Vrasku). If you take an Uruk captain with a shield, he'll have D7 as expected.