I imagine that's the only way to get someone to commit 100M+ in a seed round though.

I mean sure... but they now each have ~$30mm in (nominal) equity having done 0 work. That's not a bad deal.

by the time any average series E IPOs, they're all diluted like crazy anyways

I'm about to do similar...

Its that, or I DIY my product.

Either sounds fine to be honest.