I break out Gemini 2.5 pro when Claude gets stuck, it's just so slow and verbose. Claude follows instructions better and seems to better understand it's role in agentic workflows. Gemini does something different with the context, it has a deeper understanding of the control flow and can uncover edge case bugs that Claude misses. o3 seems better at high level thinking and planning, questioning if it should it be done and whether the challenge actually matches the need. They're kind of like colleagues with unique strengths. o3 does well with a lot of things, I just haven't used it as much because of the cost. Will probably use it more now.

I don't think it's simply a stylistic matter: it seems reasonable to assume that text in books tends to have higher information density, and contains longer and more complicated arguments (when compared to text obtained from social media posts, blogs, shorter articles, etc). If you want models that appear more intelligent, I think you need them to train on this kind of high-quality content.

The fact that these tend to be written in an older writing style is to me incidental. You could rewrite all your college text books in contemporary social media slang and I would still consider them high-quality texts.