I think a fair compromise would be if you catch a ban evader. You're able to place a temporary ban of 48 hours on the accounts to be reviewed by a more senior staff member in that time frame.
If the senior member agrees with the decision, they extend the ban to permanent, if they disagree they revoke the ban and the user is allowed continued usage of the site? This way a "four eyes" principle is used and no one can complain as the ban would be actioned by two staff members.
I imagine that Sythe like other boards I have monitored has a staff notes section on each users profile (one that records can't be deleted from) Once a staff member has actioned a ban on the account, then the staff member will need to record a note on the players profile with sufficient evidence of the ban for other staff members to view. Then if there's an issue/discrepancy the staff member concerned can be coached on how to manage the situation correctly going forward.
There shouldn't have to reports from other accounts for a staff member to take action on another user if rule-breaking is evident. If so, why have a staff team in the first place?
If the bans are consistently wrong from a single staff member, then obviously, there's a problem afoot for the management to take up with that member concerned and revoke their privileges if necessary.
I honestly see no harm that can be done here assuming the staff that get this power have sufficient tools to make sure they are correctly banning accounts.
I've already told staff multiple times if they want to ban people who are evading, they need to create a report in "Report a Ban Evader" section with sufficient evidence without the use of staff tools (IP audit, staff lounge, etc.). Their argument to this is simply, "That's a waste of time. I can do it myself." In saying that, all reports created by regular users are then a waste of time, which isn't the case. Of course to that they might say something like, "Well that's not how I feel. You're taking things out of context.", but I'm not. It's to reveal how much of a waste of staff time and site resources are to "headhunt" for ban evaders in a staff capacity. Ask yourself what's really being accomplished in doing this.
Why have a staff team with access to these tools if they're not able to utilize them in the correct manner by banning accounts that are breaking the rules and they have to report them as any other regular account would? Surely the access to these tools would make their jobs much easier, as staff they're already trusted to a sense to make a correct judgment call. If the staff tools make it easier to spot an evader, let them use them to that effect?