This is not a moral question of who deserves what. Compensation is a business issue, not a moral one.
The question is whether OP is getting as much as he could get elsewhere, and the answer is likely "no".
If startups could compete fair and square with non-startup comp, employees like OP wouldn't be discovering that their equity stake is tiny and they are therefore underpaid after 5 years of working for the same startups every day.
> Put yourself in the shoes of the owner who took risk up front.
Why should he? Is this "would-be millionaires sympathy hour"? You're saying the founder took more risk. Maybe he did. That's actually not always the case, when you factor in opportunity cost for a non-technical founder vs an engineer - I've seen founders earn as much as they would elsewhere in base salary, without factoring their enormous equity at all.
But even if the founder took more risk, how does that compel OP to work hard to make him a millionaire, while foregoing fair market compensation for himself?
You are implying it's OP's moral duty to compensate the founder for the supposed risk he may (or may not) have taken.
OP's only duty is to do what's best for himself. The founder and investors are certainly doing that by making OP work weekends for what is likely below-market comp.