"Flat design" is, yes. It's just a horrible label for a much broader concept, which is "form follows function", "clarity", "honesty".

Skeuomorphism is an easy target because it is dishonest by definition. Things that appear "cutting edge" or "high quality" today will, in a few years, seem dated, clunky, and pointless.

By contrast, pick up a copy of Die Neue Typography and see how well not just Tschichold's designs, but his ideas, hold up today. Skeuomorphism is a symbol of the Old UI. What we need is the New UI.