Very little

Zero.

the foundation didn't exist so that one staff member didn't exist. the foundation doesn't direct development either, they sponsor development and otherwise help to fund the project.

there is not fault either. hhvm was never a php project. they happened in parallel and there was a lot of good feelings at the time and efforts to collaborate. facebook ended up releasing hack lang and the projects drifted apart.

What, so if Meta can throw enough money at it, they can just hijack the project?

I see your point, but we shouldn't allow corporate interests with comedic amount of economic capital to simply take over an entire project through what basically is ye olde EEE tactics.