The recourse for a power-abusive SO diamond mod is to contact Stack Overflow the company through the contact us form and explain your grievance.
The number of moderators on Stack Overflow (and the rest of Stack Exchange) is significantly less than those on Reddit and the standards that they are held to are much higher, the tools that they are given are much more powerful, and the expectations of their conduct is also much higher than Reddit.
If you see a diamond moderator violating anything described in that contact Stack Overflow (the company). There are serious repercussions for a moderator violating that.
Note that this only applies to moderators - those users who have a diamond following their name. Other users are not moderators (and this is one of the sources of frequent confusion - terming anyone who can vote to close a question as a moderator).
The number of moderators on Stack Overflow (and the rest of Stack Exchange) is significantly less than those on Reddit and the standards that they are held to are much higher, the tools that they are given are much more powerful, and the expectations of their conduct is also much higher than Reddit.