Again, history says otherwise. Arianism only appeared with Arius. Prior to that it was the teaching of the Trinity that was within the core of orthoxy - by your definition - it was popular. Prior to Arius were the various gnostic sects that attempted to appropriate Christianity as its own with their aberant teaching on God. Gnosticism never gained traction within orthodox Christian teachings - never 'popular' by your definition.
So if Trinitarism was not 'popular' cite sources for what WAS more popular then.
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Actually the word “Trinity” never shows up in New Testament writings or any of the early church fathers until nearly 300 years after Christ, when Tertullian coined the term. While it is true that Arius’teaching of Christ being the first creation of God was rejected in the first council of Nicea it was a popular belief.
There are many hints of the belief of the doctrine we now call Trinity in the early church writers, especially John but they are vague and ill defined. In my opinion while those hints exist and I fault nobody for coming to the conclusions now popular I think there is more evidence that the 1st century beliefs as shown in the Gospels is more likely correct.