I think it's more nuanced, and goes beyond just the content of the quoted excerpt. While copying the features (acceptable market competition), did Facebook leverage/abuse their monopoly status to prevent users from migrating to the upstart with better features? Further, are users being kept on Instagram using better features, or by abusing network effects? If it's the latter, then I would consider that a clear target for antitrust litigation. And preventing users from switching products while you catch-up (or not) seems squarely in that ballpark.