This is definitely something that we will need to look into before migrating to OJS 3. Many mid/large journals (and even lots of small ones) will have separate journal admin teams vs the editorial teams. Having only one permission level will mean that they will both see irrelevant options to their role. Many editors will also not know the intricacies of the management settings and thus journals are more open to errors being introduced by editors taking tasks upon themselves when theses are supposed to be controlled more centrally (e.g. as a publisher, we need to be involved in policy decisions). Even if some editors do need to have the journal manager permissions, it is still likely that this would be on an individual basis and not applied to everyone at the editorial level.
If nothing else I want Editors to focus on editing and not have the distraction of journal management, and I want journal managers to not have their interface diluted by editorial handling data, unless the settings/data are relevant. The OJS 2 division dealt with this very well, as it allowed each permission to be assigned on a user-level, providing the flexibility needed for different journal needs. The all or nothing option in OJS 3 will mean either a lot more training or trust that editors won’t click buttons that we don’t want them to.