Where do you find that the teaching was wide spread and accepted? According to the historical records, it was only accepted in the Alexandrian diocese and was spreading in African provinces as well, Arian was said to teach sailors the teaching as sea shanties in a hope of spreading it. When it came to the ears of the other Bishops, they universally condemned it although Arian claimed to have many believers, of the 300+ people at the First Council of Nicaea, only 22 initially were supporters of Arian, although it is clear some only supported him for personal connection and political reasons, after months of debate he had only 3 supporters, the rest signed off on the Nicene interpretation of Christianity.
Moreover, what Arian claimed was not the modern teaching from WTBTS that Jesus is Michael, just one of the many angels, subservient to both God and a delegated co-ruler with the “anointed ones”, he still saw Jesus as divine, connected to the God-figure which he believed to be infinite whereas Jesus was still a (part of) God, but a finite one.
In a sense Arius did not reject the trinity, his writings seem to point that he tried to combine the scripture that support the trinity and scripture where Jesus at face value seems to reject it, by saying the trinity was created by a greater (aspect of) God and then that that character became the Father that created (begotten) Jesus but Jesus does not know this (the entire idea is rather fractious and esoteric, between partial writings that survived).
The complete rejection and claim that the Father was not part of and greater than the Son came after Arius death, Arianism had survived in some churches and was taken up and driven in the empire by Justin the Apostate that wanted to bring back the controversy to break up the Christian Church and bring Roman paganism back to the Empire, clear to see, Justin did not succeed and the Nicene viewpoint prevailed.