This person created this valuable asset, giving his time and effort. The other person's effort to create it might be non zero but so are OP's and therefore, there is no reason why OP should walk away from it.
It’s a calculation. And it’s not a binary fight-or-flight situation. There’s room to maneuver - legal maneuvers, speaking with the investor, etc.
These comments here merely suggest that the goal should be to fight for what the OP rightfully earned, and that hostile actions and a threat for war should not be left unanswered if you have the capability to answer, both in order to retain the value the OP has at this moment and in order not to hinder their reputation in future endeavours - and, also very important, to have peace of mind (sleep at night). Feeling like a piece of sh!t guarantees lifelong bad sleep nights, incomparable to having to wake up early to go to the court.