People underestimate the importance of speed on quality of thought, because people underestimate just how much quality is a result of simple iteration. When an LLM thinks, it typically just makes one pass. It outputs tokens from top to bottom, beginning to end, and then it's done. But when people think, especially strong thinkers, we typically iterate and revise our thoughts on the fly. We do numerous passes. We stop…
...it already is, via thinking/effort. That wouldn't be possible if a LLM at usable quality wasn't fast enough to allow at least some amount of "thinking" (i.e. hidden text generation).
But your point still stands: we could get massive quality gains by allowing even more thinking by default, if it was fast enough.