Manchu Ideas are better. My argument: -20% Core Creation Cost.
Manchu ideas might be the best non-formable ideas in the game.
Manchu is formable. Unlike earlier patches, it's not even limited to the Jurchen tribe starts. If you want, you can form Manchu as Poland, though that will probably take you a while.
And yes, their ideas are fantastic for WC. -20% core cost coupled with -10% tech cost and -2 unrest is a great pairing. I put the set ahead of Rome and Italy, about even with Mughals, and a bit behind Yuan among formables. Access to banners isn't technically part of the group but is also amazing.
*Rival AI allies another rival AI so they can stand a better chance against the player menace* - "OMFG, unplayable! AI should not do anything even remotely clever!"
Too bad for the AI, it still vomits guarantees all over the place completely undermining its own alliance logic as the player simply cancels them then dismantles before they can re-establish it.
So please, armchair commander, what else could I have done to prevent this?
Pick Bohemia instead of picking Austria and win your own wars if you must, which was the opening that led to my position earlier in the thread. Bohemia did help distract Denmark at one point though, you get favors with them pretty fast.