You wrote: "My reading of this suggests it to be a statement that Jesus is not a part of a trinity godhead, I think this is just as well backed up by the Christian bible too. He did not, at least in this passage, challenge Jesus' credentials as the "messiah" just the belief in his equality with God."
5:71-75 is stating the Islamic belief about the aloofness of God and the station of Christ:
- Allah (God) is not the Messiah son of Mary (= Jesus)
- Following from that: Allah is not a trinity, he is One.
- As you can see, the Messiahship is not doubted, in fact it is reaffirmed. The return of Jesus is one of the salient messages of Islam.