This will be controversial as it balances heroic efforts of founders vs the less risk-taking yet sizeable community who are 99.99% necessary to follow them. Overall theme is, what you did as a founder is great and you should be rewarded, but even 10% is pretty unfair and suffocating dead weight to the people who likely need to come after. You want ownership in something that succeeds.

1. This is why 4 year vests are critical. For co-founders, IMO, 4 year really should be 6 year. So 40% should really be 10-20%.

2. Focus on good/bad cases. Frankly, the value of OP's contrib is high wrt current company, and low wrt the necessary work to be done and effort/risk compensation for the people to do it:

a. Failure -- who cares. This is the 95% case.

b. Small exit -- so let's say they get releaseable (tech), enough micro-pivots to solve early product/market fit (product), get early traction (marketing), some sales, some hiring & management, and given current state, more investment by co-founder. WOW that's a lot of time/$/work still to be done, say another 2 years and maybe now it's Jim and a few contractors or ever 5-20 people, to get to a small M&A. Those folks will be taking low pay, hard hours, & a ton of risk, and they can't all get 10%. If a $5-10M exit through that many other people and investors, how much is OP really responsible for, $1M? $500K? IMO most of the hard work is still to be done: initial app launch is pre-product-market fit and pre-traction. This is the 4% case.

c. Big exit -- First they need to do above product/market fit iterations, could be a couple years. Then they need to build the actual business. So they bring in investment and build an operational & growing business. Let's say 1-3 rounds @ 20% dilution each. Takes another 5-9 years over ^^^: figure out sales/marketing, turn that crank, hiring, a pivot mid-way through, etc.. And exit at 50-200 employees for say $100M. So much more work to be done. A lot of people's work to pay out on: if everyone got 1%, wouldn't be enough. Arguably your 2yrs is worth than a senior infrastructure engineer spending nights and weekends for 2yrs replacing your code so it could scale to 10M people, but is it worth 10X more? 100X more? Riding the labor of others to the tune of $1-2M is just 1-2%, so starting with 5% now is still great.

3. Future investors and acquirers may look at the cap table and see OP's dead weight on it. It's very solvable.

"5%? That'd be equity for 10-50 employees, who is this person? Let's agree to a smaller acquisition with small/zero payout, and invest in that new company."

Or "5%? As an acquirer, we want to pay the people we're trying to sign on to our team, not some dude on a beach who wrote some stupid app that isn't even what the company does today, let's shift proceeds to sign-on bonuses." So weirdly, in your favor not to be big dead weight. Even 10% is dead weight.

4. For remaining founder, so much heavy lift & investment & risk is still to go -- esp if a 5-9 year journey from here -- that 20-30% is demoralizing. Let's say they want to hire another CTO and give them say 20-40% (VESTING!!!). So your remaining cofounder has to do a huge years long lift for... 20%?