Even assuming that the four gospel accounts were not written by eyewitnesses, the conclusion that they are rubbish or inaccurate does not follow. A secondhand account (such as Luke) is not unreliable as long as the writer works closely with the original eyewitness. We do not doubt biographies that are carefully written. Eyewitness accounts are trusted on a daily basis in courtrooms.
Moreover, the four gospels were written during a time when people committed to memory lengthy speeches upon hearing them. Consequently, it is not reasonable in this scenario to simply dismiss the memory of the eyewitnesses to the risen Christ as unreliable.