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.