What are the differences in how women are treated in Islam compared to early non-Islamic rights?
The truth is, we do not know very much about pre-Islamic Arabia, because there were so few written records.
The pre-Islamic Arabs would kill babies whom they could not afford to feed, and they killed more girls than boys. Islam forbade this practice, which was a definite plus for women's rights.
Islam specified that a girl could not be married against her will. However, the law was designed in such a way (silence implying consent) that a girl with an overbearing father had no realistic legal redress. In practice, therefore, Islam has permitted forced marriage. It was probably much the same before Islam, but we don't really know.
Islamic law was much more specific than previously about financial rights in marriage, e.g. whether a woman should be paid a dower and how much. This made life better for the wives of mean men. However, the Islamic provisions were not particularly generous, so they probably did not make much difference to the life of the average woman.
Islam encouraged minor wife-beating but discouraged major domestic violence. This was designed to make life better for the wives of cruel men but more orderly for strong-willed women married to easygoing men. In practice, however, there was no penalty for a man who beat his wife "too hard" - he was not even to be asked why he had done it. It was on a par with a man who starved his horse: decent men agreed that it was a wrong thing to do, but the bottom line was that the horse was the man's own property. So the net effect of Islamic law was to encourage wife-beating, and some remarks made by Ayesha suggest that Muslim husbands overall were crueller than their pagan neighbours.
Pre-Islamic Arabia permitted some forms of polyandry as well as polygyny, with the result that female adultery was taken less seriously and probably did not attract the death penalty. Islam forbade polyandry and killed adulteresses. However, a man was only considered an adulterer if he stole the wife of another Muslim; he was permitted to marry up to four wives at a time, and to sleep with as many non-Muslim women as he could capture in a war or buy on the slave market. In practice, not many people of either sex were executed for adultery (although more women than men) because it was so difficult to prove. But everyday jealousy would have been a major problem, as a woman could not even speak socially to other men, whereas a man could have sexual relationships with multiple women. While polyandry and prostitution are not particularly beneficial to women, they are not as bad for women as the Islamic system that replaced them.
Pre-Islamic Arab women were able to move freely about the town. For example, Mohammed's first wife Khadija was a merchant. Islam ordered a woman not to leave the house without her guardian's permission. While this might have protected women in a time of war and disorder, it greatly restricted their right to move even in periods of safety. It did not occur to the Muslims to preserve women's freedom AND safety by making rules that restricted men from harassing women. This was definitely one way in which Islam restricted women's rights.
Islam does not specifically forbid a woman to have a career. Three of Mohammed's wives were tanners, and they continued to work from home after marrying him. His wife Ayesha was a teacher. She hung a light curtain over her classroom door, and men sat outside the room to listen to her teaching, hearing her quite well although they could not see her. However, the rules about not leaving the house and not speaking to men definitely made it much more difficult than formerly for women to have careers. This limited both their financial independence and the interesting activity in their lives.
Women who were the mothers of sons and who lived to be old were treated with great honour in both pre-Islamic Arabia and under Islam. Probably not much changed there.