The Balrog is an independent agent of evil-not essentially under Sauron's will,
since it was a Maia itself.
I'm willing to bet that Sauron had an Easterling general or a Morgul-lieutenant
leading the Dol Guldur forces. He didn't know but suspect that Galadriel was a
Ring bearer. Plus, his will was bent on tearing Minas Tirith apart- those he
sends there are his own armies, while the other armies are his allies and not
his own forces per
se.
There is but one task remaining in Arda-we,the Dragons of Valinor will make it happen.
Lone resident of the Republic of Gondor
PO-TA-TOE-S not PO -TAH-TOE-S!