I suppose that it is, in the widest sense of the word.
However, I thought you were using the word in a much narrower sense. You specifically mentioned the three "ecumenical" creeds: the Apostles' Creed, the Nicean Creed, and the Athanasian Creed. These are formal, authoritative statements of religious doctrine promulgated by councils of churchmen and scholars.
My understanding is that "non-creedal" churches reject the formal creeds, presumably including the Apostles' Creed, the Nicean Creed, and the Athanasian Creed. Since you stated that acceptance of these creeds is required for one to be considered a Christian, I was wondering whether non-creedal churches are Christian in your view. Apparently you consider them heretics, unless they would agree with the content of the creeds.
Personally, I can accept the Apostles' Creed, although Mormons do not use it. Most of the Nicean Creed I can accept, but it contains a few points that I do not understand and some that I do not accept. The Athanasian Creed is completely incomprehensible to me.
Do I fulfill the creedal requirements for being a Christian, according to your definition?
For me a Christian is a Trinitarian. Do you believe in the Trinity?
If you were part of a creedal church which systematically taught you these things it might not be much of an issue. Folks have been making sense of these creeds for centuries. They have been part of the foundation of the Christian faith.
Apparently you consider them heretics, unless they would agree with the content of the creeds.
That is correct. They may not formally need to paint the creed on their building, but they need to agree with the the subststance of the creed, otherwise they are, by definition, heretics.
Churches can get into trouble when they try to nuance things under their "No creed but Christ" meta-creed.
OTOH, JW and Mormons are outright heretics by the historic creedal standards. By the standard of the meta-creed they are brothers in the faith.