The main counterpoint I'd try to come back with would be that apps arent special. For almost all apps, the apps highest service is to fade into the background, to become undistinct & not noticed. Cute might possible draw some early smiles for a little, but for anything enduring, cute tends over times towards noise & pointless distracting & unwelcome character.

There were some real losses though. The tension between flat & unobtrusive vs flat and indistinct becomes a usability issue. Clear separation of elements & sufficient contrast can be lost.

In some ways, it should be more a question of what the user wants. Apps used to sometimes have multiple skins, winamp being an over the top notable one, but I believe IM programs like trillian did too. The old gtk2 themes on linux allowed users far more flexibility in picking what kind of an experiemce they wanted, what level of contrast they wanted, what the look & feel.would be like. The alow march towards everyone being beholden to crazy crafty designed UI's we were force fed is, imo, part of what drove the counter-push towards flat; users lost control, it was way too overloading an experience, and flat became the more neutral acceptable dictated/company-driven style.