Well, the Filioque is a rather big exception, considering the role it played in the schism between the Eastern and Western Churches.
Interesting question, but a red herring in the present discussion.
Not at all. Any definition of Christian which excludes the early Apostles and saints strikes me as absurd.
The Nicene Creed is the official creed of the EO, but I’m not aware that the EO would deny anything in either of those other creeds (with the exception of the Filioque).
What about those Protestants who claim to be "non-creedal"? Are they Christians according to your definition?
No one is excluding anyone. The question is a red herring because it makes no sense. The creeds as we have them today did not exist at that time. It is like the old Saturday Night Live sketch, "What if Spartacus had a Piper Cub?"
However, since the creeds are built on the testimony of the apostles (the Bible) and the early church we have confidence that they are correct in all they teach.
What about those Protestants who claim to be "non-creedal"? Are they Christians according to your definition?
Any "protestant" who could not affirm the statements in the ancient creeds cited should have their Christianity questioned. There is much bad teaching among the "no creed but Christ" crowd, including poor constructs on the Trinity that lead to a form of modalism. The very purpose of the creeds is to sort out the bad theology among the faithful. And to help keep cults and heresies (wolves) away from the flock.