The pike is only a C if the gainer is off the end of the beam, with your head close to the end of the beam. Off the side of the beam, its an A.
This dismount off the end is not easy, it takes a lot of time to develop for safety reasons! Lots of work tossing the gainer straight out, landing on the back on a big resi mat, then adding the height to add the flip much later.
My thoughts: if you arent at the skill level to do a round off on the beam, you are not at the skill level to do this dismount safely.