The angel has little power against later VC rounds besides the protections he negotiated for upfront. Since it's purely in the VC's interest to screw the angel

The angel has little power against later VC rounds besides the protections he negotiated for upfront. Since it's purely in the VC's interest to screw the angel, the angels make it a standard to negotiate this protection. And of course people get upset when a negotiated protection is tossed aside.