That makes no sense. The big labs don’t reveal their efficiency research but that doesn’t mean they aren’t doing it. They can charge the same prices while making models more efficient internally and increase margins…

I bet they do that as well but I also think that if they have to choose between inference speed or "intelligence" they would choose the latter.

They don't have to choose, though, since they can release multiple models with different tradeoffs.

This would imply they have infinite development capacity

Not infinite, just enough to make more than one model. OpenAI and Anthropic both have four different size categories...