Mercurial is generally believed to be simpler and easier to learn than Git. In turn, there is often the perception that Git is more flexible and powerful. This is due, in part, because Git tends to provide more low-level commands, but also in part because the default Mercurial tends to hide advanced features, leaving it to users to edit the mercurial config file to activate the advanced features they like. This often leads to the perception that advanced features are not available in Mercurial.
Mercurial has always focused more on interface aspects, which made it originally easier to learn. In comparison to Git, a shallower understanding is required to operate with Mercurial in a useful manner. In the long run, such encapsulation has given Mercurial the false appearance of being less powerful and featureful than it really is.