I'm not sure about the idea that there was no Christian standard. Paul wrote the earliest books, and he wrote in 2 Thessalonians 2 that the "mystery of iniquity" was being held back until the one "acting as a restraint" was out of the way. He was referring to the apostleship as the restraint, and as a warning for when they are gone he tells them to stick by the teachings they received "from us" or the apostles (2 thess 2:15). This sentiment is echoed in Peter 1:15, where the writer insists they should stick to the apostles teachings after they are gone. He then goes on to show why by warning about how devious the false teachers would be in chapter 2.
So being that they directed fairly early for the first century christians to only listen to their teachings and stick to them once they died, this demonstrates a standard - the apostles teaching about Jesus. It was not to be changed or replaced. The things that went beyond these teachings or were questionable were left out of the bible. We have the gospels, likely based on Q material which was a fairly early sayings gospel, we have the record of deeds following christs death, and letters to the congregations they established. It's all information from the apostles.
Anything written by anyone else is useless (anything related to teachings and doctrine). Per their own testimony (2 Peter 1:15; 2 Thess 2:15). (Also I say this as from the bibles perspective)