I would, but Bel-Gond is currently setting up to ensure that the gatehouse remains in orcish hands. While it is true that it is currently the easiest place to defend, all it would take is one or two people to open the gate and provide the humans outside an opening to charge through. Doesn't even need to be one of the attackers; There are plenty of humans inside of the fortress who would [i]happily[/i] welcome in a human army over an orcish one, even if that human army doesn't exactly have their best interests in mind...

Besides, Bel-Gond is made for defensive fighting like this. Just tell him where to set himself up and he'll make damn sure nothing gets by him while he is alive... and his dwarfish blood will make damn sure he sells his life for a damn good price.