Two things I noticed that were flawed. Humans are as far as I know, forerunners. This conclusion is brought on by the statement made by 343 before his termination in the end of the third game. He very clearly said YOU ARE FORERUNNER. Also The part about it being impossible that it is a forerunner is also flawed due to the possibility that forerunners could be trapped on the planet you are apporaching and were unable to leave the atmosphere due to destroying spacecraft to stop flood, loss of technology etc. We know the planet is not ONYX because as I read somewhere else on these forums, it was destroyed.