What would they have to do to appear unbiased but still be able to release information damaging to the DNC and Clintons?
If they only used Twitter to make announcements and highlight interesting documents, I think they would be orders of magnitude more trustworthy. Let the documents speak for themselves, and let other people write the commentary.
If they are truly unbiased, they should release all the information they've got at once; or hold onto it until after the election; or also release other information they've got about Trump and other countries. Let the readers decide.
The fact that they release the emails in daily batches clearly shows they have an agenda and want to influence the outcome of the election. Which is fine, if that's what they aim for.