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.

Their interest in correcting your grievance is directly proportional to your ability to cause them trouble if it remains uncorrected.

I have zero capability of causing them real trouble, and they therefor have zero interest in correcting anything.

Likely, few people have non-zero capability when it comes to causing them trouble.

> and the standards that they are held to are much higher,

I've seen no evidence of that.

The moderator agreement is viewable at https://stackoverflow.com/legal/moderator-agreement . There is nothing equivalent on 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).