Marx underestimated both groups because he spent 99% of his time on his fat ass, reading and writing. He never did visit a single factory.
He thought that the bourgeoisie were too horrible to help the poor, which they werern't. The bourgeoisie was the source of whatever charity there was. Also, the great societal reforms came out of the Christian churches, ususally led by vicars -- who, more often than not, came from the bourgeoise class.
He thought that the proletariat was too stupid to learn or make their lives better. They DID manage to unionize and make their lives better.
Marx's babble about the thesis/anti-thesis with his own thesis of communinism being the ultimate and undisputable thesis was arrogant, ill-thought out and a masterful example of not having CLUE ONE about human nature.
Marx's theories require a totalitarian, utopian society, because it looks on man as being a hive creature, no different than a worker ant or bee. And if you don't want to participate in the utopia, you must be eliminated.
Mark