Of course all slaves were not submissive. This may have been the view that scholars held in the early parts of the 20th century, but it is certainly not a view that is held by any serious scholars today.
Today, we emphasize that there was a great deal of resistance on the part of the slaves. There were the overt sorts of resistance like running away, but this does not tell the whole story of slave resistance. Scholars today emphasize that the vast majority of slaves resisted their masters in more subtle ways. For example, it is commonly said that slaves worked slowly, broke tools, and feigned sickness. In these ways, slaves used whatever methods they could to resist their masters.
We no longer speak of slaves as having been helpless and submissive. We now emphasize all the ways in which they fought back against the oppressive system in which they were caught.