I think Rationalism is a bad policy tree currently.I should have guessed because you said you didn't use Rationalism :O
Btw why not Rationalism? Not saying it is wrong, for me Industry is usually a default choice for Diplo cause you need that extra gold and production. But in your particular case you may take Rationalism because you already dominate all City-States and you want to get to Atomic Theory ASAP to unlock UN...
It gives a lot of +% to science, which won't affect my trade routes anyways. Industry's +2 trade routes alone give me 80 science from UA, and even more science and culture for the trade route itself. Though honestly imperialism would probably have been better. I am building everything really quickly so I didn't really need industry, I settled two cities with pioneers and they have basically caught up to my other ones.