While both women and slaves suffered, slaves clearly suffered more egregiously than did the white women for whom Wollestonecraft advocated.
From the beginning of Equiano's narrative (and throughout much of it), the physical horrors are shocking, beginning with the former slave's capture and transportation aboard a slaving ship (Chapter II). Equiano recalls:
"I was soon put down under the decks, and there I received such a salutation in my nostrils as I had never experienced in my life: so that, with the loathsomeness of the stench, and crying together, I became so sick and low that I was not able to eat, nor had I the least desire to taste any thing. I now wished for the last friend, death, to relieve me; but soon, to my grief, two of the white men offered me eatables; and, on my refusing to eat, one of them held me fast by the hands, and laid me across I think the windlass, and tied my feet, while the other flogged me severely."
If you are looking for parallels, it won't really be in the physical treatment of slaves vs. women in the Romantic era, but rather the concepts of what makes a man a man or a woman a woman. Both slaves and women tended to be infantilized, that is, thought less mentally acute and emotionally less competent than free men (in Equiano's case) or women. Here is Wollestonecraft speaking to those lesser-expectations for the "fairer" sex:
“My own sex, I hope, will excuse me, if I treat them like rational creatures, instead of flattering their fascinating graces, and viewing them as if they were in a state of perpetual childhood, unable to stand alone. I earnestly wish to point out in what true dignity and human happiness consists - I wish to persuade women to endeavour to acquire strength, both mind and body, and to convince them that the soft phrases, susceptibility of heart, delicacy of sentiment, and refinement of taste, are almost synonymous with epithets of weakness, and that those beings who are only objects of pity and that kind of love, which has been termed its sister, will soon become objects of contempt."