You are right in the general case. But terminals are a specific niche, not requiring the full extent of text rendering edge cases as a browser, wysiwyg editor, etc “experience”. It renders “strictly”* monospaced fonts, which makes it trivial to cache and parallelize.

* as it was brought up, one might use a non-monospace font, but that case can just use the slow path and let the “normal” people use a fast terminal