Marx's analysis of Capitalism and predictions of where it heads are proven more correct with the passage of time. The reason the Proletarian is exploited to a greater degree than the serf is due to the nature of commodity production. As the M-C-M' circuit, whereby M is an initial sum of money, C the commodity produced with M, and M' the greater sum of money after selling said commodity is the basis of Capitalist production, said process is incentivized to be maximized. In Feudalism, rent is extracted and the rest kept for subsistence, in Capitalism wages are set by cost of continued existence and replacement, moving up or down mostly by societal norms.

Question 8 : In what way does the proletarian differ from the serf?

Answer : The serf enjoys the possession and use of an instrument of production, a piece of land, in exchange for which he hands over a part of his product or performs labour. The proletarian works with the instruments of production of another for the account of this other, in exchange for a part of the product. The serf gives up, the proletarian receives. The serf has an assured existence, the proletarian has not. The serf is outside competition, the proletarian is in it. The serf frees himself either by running away to the town and there becoming a handicraftsman or by giving his landlord money instead of labour and products, thereby becoming a free tenant; or by driving his feudal lord away and himself becoming a proprietor, in short, by entering in one way or another into the owning class and into competition. The proletarian frees himself by abolishing competition, private property and all class differences.

-The Principles of Communism

The serfs did not have it better, of course. However, the nature of their production was limited to the low technological development of the time. With mass factories Capitalism was transitioned to, and now with complex development of production in the hands of massive, monopolist syndicates and cartels, we can move beyond Capitalism to Socialized prodiction, central planning and public ownership, far easier than ever before.

I highly recommend those interested to check out my Introductory Reading List on Marxism.