Suppose, surviving from ancient times, we found four manuscripts about the life and teachings of Rabbi Hillel. These works were all written within, oh, say, 70 years of the main events of Hillel's life. They are similar in a number of ways, although each written from a somewhat different perspective, with some differences of detail. They are all written by people who were clearly from the School of Hillel, by people who wanted others to accept the teachings of Hillel. However, they claim no miracles at all. Manuscript evidence shows goes back into antiquity and assures us that what we have today is very close to the original autographs.
Would we say "Gosh, we really do know a lot about Hillel here. There are a lot of things we can be reasonably sure of about him, especially where the accounts coincide." Or would we say "Just propaganda. We need some independent sources, from people who weren't from the School of Hillel. Then we'd have some real information."
It's hard to imagine the Bart Ehrmans and Rudlof Bultmanns of the world being so skeptical if the Gospels were about a non-miracle-working Hillel, rather than a miracle-working Jesus.