Who were the Nazgul?

[Raynor]

I think Erik Tracy has explained Tolkein's work in a balanced way, & in a good context.

Since Tolkien's writings, even his speculations, take precedence over any other person's ideas, it is therefore a good practice to state the source of your quotes, as most, if not all, the members of this forum would interpret an unsigned quote as belonging to Tolkien. I know I did until I looked it up.

they did not have a great part of their original strength taken away from them like Sauron did either.

But Melkor and Sauron lost a great deal of their power in evil deeds; since the the balrogs too were heavily involved in evil deeds, their power must have diminished in time too, esspecially if they engaged in procreation, as Tolkien speculated in Myths Transformed.

In terms of commanidng will, why would a Balrog submit to Sauron given the circumstances of power each has?

We don't know under which circumstances a balrog submits, or when this particular balrog would submit. For all intents and purposes, Sauron inherited Melkor's place; for all we know, balrogs respected their master's will in all instances - I would expect them to recognise Sauron's authority too. I am not aware of any case in which a former servant of Melkor challenged Sauron's 'rightful' place.