Would pure rationality have severely limited the advancement of technology?

I doubt it. Technology is a tool, and turning down tools doesn't sound that rational as rules of thumb go. If there's some strict advantage to not using technology a lot of the time (like playing to our evolutionary preferences or something), you should still have it around even if you keep it locked in a vault. Still, you'll need it eventually to stave off some mortal sickness or asteroid or to avoid the volcano that's set to explode in six months, etc. I imagine our hypothetical purely rational agent would be far better than us at managing dangerous tech.