Advantage over others is not the only thing people care about.
The “rationality” developed in secret is unlikely to grow more powerful than whatever technology a single farmer from Dark Ages could develop in a lifetime, that is to say not impressive at all.
Regarding the second point: that’s why Guilds were created, and they were quite powerful in their day. Why do you think they’re called ‘trade secrets’?
Two things:
Advantage over others is not the only thing people care about.
The “rationality” developed in secret is unlikely to grow more powerful than whatever technology a single farmer from Dark Ages could develop in a lifetime, that is to say not impressive at all.
Regarding the second point: that’s why Guilds were created, and they were quite powerful in their day. Why do you think they’re called ‘trade secrets’?
But modern technological civilisisation didn’t take of until the guild system (keep it secret) was replaced by the patent system (publish it)