If the side project has significant costs that they'll cover, that changes things drastically. Assuming not, then the obvious question is whether you can grow revenue to 330k in two years to break even on the 50k/year loss implied by the current offer. On the face of it, that sounds really hard to do, but maybe not if your new employers have lined up a marketing team.

It's a cut-and-dried VC prop. Give up control to work on something full-time. It's many a SWE's dream to work full-time on their side hustle. Doesn't sound that way for you.