People keep saying this person has nothing to lose, but that's obviously not true. I think comments like these are mostly based on we, as a "technical cofounder" cheering section, want to see happen in the world. What's important about that is that the outcome for this particular person is an externality to us. If the whole company blows up and all equity is worth zero, that's great for the cheering section, even if it's obviously worse for the technical cofounder.
I think this is a reasonable point and depends a lot on the OP's financial situation (and it sounds like OP's is better than the non-technical cofounder).
If they're reasonably secure they have more ability to fight for a better outcome, risking the 3%.
I would do that myself because having a cofounder tell me 1 month before vesting that they want me to leave with less than half of our deal is unjust and wrong. I'd do what I could to avoid that outcome, if the company blows up as a result it's the cofounder's fault - I'd sleep fine.
I would never do what the non-technical cofounder is doing to someone I partnered with.
