Clearly they're positioning it as a mid model.
Which is in itself a bit weird as mid models nowadays are a golden mean fallacy. Terra is much less popular than both Luna (cost-sensitive) and Sol (performance-sensitive).
Claude Sonnet is a weird exception to the mid models because Anthropic doesn't do much with Haiku and Opus is too big.
It's a little of the opposite to what you're saying. By performance you seem to mean only "intelligence" i.e. pass rate. But there's a 3rd factor, time to task completion. So it's three-dimensional rather than two. And on that spectrum there are areas where Terra is optimal.
Sonnet on the other hand never is, it's far from the best pick anywhere on the spectrum.
I don’t know where you get your statistics, but I love Terra and use it all of the time. It is the default fastest model in ChatGPT/Codex today. I saw today a notice saying that the model had hit capacity briefly
But why include Opus then?