*sighs*
Smashing a pair of superstrings together wouldn’t leave much of the Local Group.
As for the second, the Severity doesn’t directly restrict Godpower usage, or the Leviathans and Reapers would be in trouble.
It makes it extremely difficult to generate and get started (to prevent races from finding out about it) and it muffles the ‘noise’ and ‘smell’ using it makes.
What you are describing are reality anchors, devices that ‘refold’ higher dimensional spaces out of the way again so that they can’t be accessed.
Once a Godpower invocation has been … built and triggered, there’s nothing aside from another one that’s going to stop it, as it pretty much makes a mockery of any rules of conventional physics or Euclidian space.
Purge the alien. Kill the heretic. Suffer not the witch to live.