No. There are no beliefs in the book. It is an economic book, and everything in it is proved through implications of axioms (mostly, the action axiom). If there are beliefs, it is in the third – and perhaps most powerful – volume Power and Market, but these points are still factual implications drawn from economic laws.
Once you start reading it you will see. Rothbard did not ruin his greatest work by injecting opinion into his treatise on economics. If there are beliefs, again, they are in Human Action, as points are sometimes presented without being proved.
The point is not who is a better economist. The point is which book is better for learning economics. MES doesn’t have the mistakes of Mises, and he adds his Theory of Production. MES was even designed as a textbook. You can learn economics a thousand times better and more clearly from MES. Further, the economics you will be learning won’t use any opinion, while even GilesStratton admits that Mises monopoly theory was “unsufficiently subjectivist”. Unsufficiently subjectivist is a politically correct term for “not fact.”
MES is an extraordinary textbook on economics. As already stated, it takes all the greatest works of his predessecors, fixes them here and there, polishes the rest, and adds the massively important Theory of Production. You don’t have to worry about opinion (unsufficiently subjectivist) or any mistakes made by being the pioneer of praxeology. Rothbard loved and reveered Mises. MES is a better textbook on economics.