Ultimately he created very little value and therefore is entitled to very little value. The company can just go out of business and start fresh!
Raising money is not value.
2-5% could be appropriate. 10% is completely insane.
The world is full of jokers talking about starting a business and jokers who have "started" a business but are faking-it-to-make-it off of credit cards. You can't do that for a 18 months. OP has built something. It may not be the software he started out to make, but it's certainly a business that some investor thinks has a chance of being a going concern.
The fact that the other founders are deciding to pivot is just a luxury of the fact that the company has inertia, not value, which is why they are switching ideas.
Our OP doesn’t want to work on the new idea, the one that might have value, therefore he is entitled to very, very little.
You do not understand the economics of VC backed startups.
If you're an exiting founder in an LLC without an operating agreement, you can kill the company. Otherwise: you leave with whatever you vested. That's really all there is to the discussion, for now!