How commonly do we Evangelical Christians determine belief based upon the following "doctrinal" foundation?

It's the basis for every Protestant's beliefs, since they have no authoritative or objective source of truth. That's why the beliefs of each denomination conflict with the beliefs of the others. It's all subjective. True authority is the reason the original and true Christian Church has been able to teach consistently for 2,000 years, without fragmenting into thousands of unauthorized conflicting manmade denominations, thereby fulfilling the clearly stated will of its founder Jesus Christ, concerning His followers - "that they all may be ONE".