> How do I negotiate a situation where I can receive the value of what I provide?
This is a good question. But before you find the answer, you have to drop the resentment. Other commenters have covered why, but if you cannot get past that, this role is not for you.
You also need to accept two important truths:
1) The success of a business is about far more than the elegance of its tech stack.
2) Your ability to re-architect a platform is not unique.
Focus on your own correlated truths:
1) The operational optimization of a business is correlated to the elegance of its tech stack.
2) Your background will make it an easier road to walk to re-architect vs. people without your background.
In short, come in showing them that you offer value above others and can help them succeed. But do not walk in as a prima donna acting like you are their one and only savior. Ask for compensation that makes the work worth it to you, but don't begrudge them their own success.
After being both a technical cofounder and a senior brought in for an MVP rewrite at different points in my career, I completely echo @codingdave’s opinion. Unless it’s the 1940s and you’re recruiting for the Manhattan Project, skill sets are not as rare as we engineers like to think.
Assuming you want the job, the goal is not only to demonstrate the value you can provide, but also the ability to build a good working relationship with the founding engineer. Regardless of his or her shortcomings, the founders will be loyal (to a point) simply because they got them this far.
Prove you have the expertise to evolve the system, but also that you can be a team player. The combination of these two traits is really what’s rare; either in isolation is comparatively common. Business stakeholders can’t really tell the difference between a mediocre engineer and an outstanding one; they can only judge their communication skills.
Whatever you decide, keep in mind that both issues—rearchitecting the product and learning to partner with its original author—present enormous opportunities for growth. It’s a rare job where you know what the challenges are going in.
Lastly, should you get an offer, make sure the salary is one you’re happy with. Equity is a lottery ticket that can be diluted or invalidated at any time. Don’t count on it.
This is a good question. But before you find the answer, you have to drop the resentment. Other commenters have covered why, but if you cannot get past that, this role is not for you.
You also need to accept two important truths:
1) The success of a business is about far more than the elegance of its tech stack.
2) Your ability to re-architect a platform is not unique.
Focus on your own correlated truths:
1) The operational optimization of a business is correlated to the elegance of its tech stack.
2) Your background will make it an easier road to walk to re-architect vs. people without your background.
In short, come in showing them that you offer value above others and can help them succeed. But do not walk in as a prima donna acting like you are their one and only savior. Ask for compensation that makes the work worth it to you, but don't begrudge them their own success.