This all depends on the shape of firms' AC curves. If the AC curve turns up quickly, large firms will be unable to survive in competition against small firms. If the AC curve turns up slowly, small firms will be unable to survive in competition against large firms. This is false.
Monopolies do more than transfer wealth from buyers to sellers.
There are also deadweight costs that arise because monopolies charge prices above marginal cost. In a small rural town 100 years ago, almost every seller was the ONLY supplier of certain products in the town. Today, even in a small rural town there are many alternative suppliers - mail order, for example. Thus, markets are probably much more competitive than 100 years ago. Therefore it's profits are positive.