The big difference is that The Bible says that we should believe blindly in The Bible.
Or rather, the first chapter of The Gospel of John says that God is "The Word" incarnated.
There is no such text-centered imperative anywhere in The Gathas. The concept of The Word does not even exist (it was rather invented much later by Plato and the Greeks in the concept of "logos").
The Gathic imperative is instead to think critically for ourselves and use our sacred minds to do so. Even to the extent that we are free to question the theories of The Gathas regarding other matters in The Gathas besides this foundation.
This is why we have no tradition of slavishly following "The Word" in Zoroastrianism. It is a very recent and limited phenomenon probably inspired by the centrality of holy scriptures in Islam, Christianity and Bahai.
And many of us are opposed to such text-centrality as principle. As you've probably noticed already.
Ideally we should test religious statements out for ourselves.
However what if we don't have the critical abilities - or what if our
cultural environment so blinds us that we can't find the way forward
by ourselves. In that case we have no choice but to look for some
authority outside of ourselves to help us. I think this is one of the
justifications for Protestants to say that the Bible is the literal
word of God. It gives them an anchor - one which can indeed be a lot
of help, even as it can be misused.
The same applies if we make the Gathas the sole authority. It is a
problem if people interpret them to fit their point of view and then
claim their ideas are uniquely sanctioned by Zoroaster.
On the other hand giving the Gathas such importance at least provides
some external reference point for people to measure their own ideas