I’m drawing on some old memories here, so I could be mistaken, but I don’t think the stack is read only, not in C anyway or in the underlying machine code. If it is faster it has to do with greater overhead needed managing the larger heap and perhaps being more efficient to push and pop with small offsets to a local stack frame vs large absolute addresses.

I don’t think they are the same category of thing. Ocean is a design system. Breeze is a theme.

Edit: now I’m less sure. This seemed to say it is both a style and a “design system” which I took to mean a technical mechanism for styles, but now i’m less clear what they mean.