[The Might]

Ares, I think you're wrong underestimating Gothmog's role.

Gothmog was High Captain of Angband and Marshall of Morgoth's troops making him basically the military second-in-command to Morgoth, whilst Sauron was also very important, but played more a domestic role rather than a front-line one.

So, these two together, were the most important servants.
Who was more important, is up for debate.