To me, it was not a question of whether he could be successful or not, it was just if he could become a legit elite QB. After his rookie year I knew he had all the tools and the talent, but I didn't know of he would realize it or not. After his 2nd season I felt better, thinking he could eventually be something consistently special. After 2020 it was clear he had arrived as an elite QB.
I don't think he was mainly bad in 2018, just inconsistent. There were times where he made the most accurate, difficult throws you have ever seen. Other times he would miss simple throws. And, he had no talent around him.