Hijacking means seizing control, and that simply hasn't happened. The prosperity gospel is a loud, media-friendly strand in some charismatic and megachurch circles, but it doesn't define Christianity's center. Catholic, Orthodox, mainline Protestant, and much of global evangelical Christianity still teach the cross, sacrifice, and care for the poor, not health and wealth as proof of faith. Someone can find a prosperity preacher on TV in minutes, but that's visibility, not ownership. A movement can be influential and still be a minority voice. Christianity has absorbed plenty of loud movements without being hijacked by them.