The statement "there is no objective system" reads like it could be a practical statement as in "we haven't built one yet", while I believe (and think the authors agree with me, based on the paragraph) that no such principled objective system can exist. Either way this should be clarified.
Three quick notes for myself as I work on this issue
We do want to claim that no single principled objective system can exist
The recent review about collaborative writing demonstrates different approaches, supporting that there will not be a one-size-fits-all solution (#110)
Now that we have more Manubot manuscript examples (#128), we can point to different strategies other groups have used to determine authorship and author order, including meta-review and deep-rules
The statement "there is no objective system" reads like it could be a practical statement as in "we haven't built one yet", while I believe (and think the authors agree with me, based on the paragraph) that no such principled objective system can exist. Either way this should be clarified.