Waaaay under built in my opinion.
Plan B looks almost worse, for basic physics reasons.
SpaceX is proposing to put around 17-20 million pounds of force onto a flat plate with holes in it. And manage to pump enormous quantities of water through the holes; NASA's system manages 500,000gpm, perpendicular to the engine thrust pattern, for lower thrust launch payloads. So that puts SpaceX in the 1-2Mgpm range through all of those holes, with far more back pressure because the SpaceX design has holes that have the entirety of the thrust acting as back pressure.
I think that NASA has the right design idea on this one...
You read it here...