Indeed, given that the texts where there are differences come from Cave 4 -— where they were not in glass jars — indicates to me that Cave 4 was the dumping ground for the “iffy” texts.
Considering that the purest form of the Word of G-d is the kosher Torah Scroll, and that they are all inevitably victims of organic decay, the simple fact that they have been copied correctly for three thousand years is sufficient.
I have a serious karaite streak in me; doubt scribes all the time.
Faith is obviously essential; faith plus knowledge (what is here) is even stronger (or easier, depending on your perspective).