It seems to be totally up to luck whether Thankmar gets anywhere near enough support to win his rebellion. Oldenburg and Franconia are the only ones who reliably join (because the coding of the event forces them to) and I've even seen Franconia immediately re-absorb itself into Germany after pledging to support me. The event triggers pretty much immediately so I have very little time to set up. I've never even seen an instance of me getting as much support as in the Thankmar's Rebellion AAR. Is there a way to reliably make it so that other German vassals like me more than Otto or will I just have to reroll for hours until I get lucky with the relations given by random traits at the start?