You are thinking about this the wrong way. From the scraps of information that we do have, which includes volumes of work by Jesus's followers, there are two extremes one could take: we know absolutely nothing about Jesus or whether he even existed, or we know absolutely everything about Jesus. I agree that the later extreme is wrongheaded, but surely treating it as a binary choice so that the only other possibility is that we can say nothing at all about Jesus is also wrongheaded.

You might argue reasonably, of course, that his followers cannot be trusted, so we can learn nothing from their writings. This is not true, however, because if nothing else we can learn from the editorial choices that they made; for example, when a Gospel goes out of is way to explain a detail that would have been embarrassing to contemporaries, this actually provides potential evidence that this detail was true and widely known at the time so that it needed to be explained, because otherwise it would just have been left out.

At the end of the day, scholarship is essentially about weighing probabilities rather than certainties, and good scholars do not pretend otherwise.