Re the question of what's on-topic: My understanding is that this kinkmeme is primarily for Captain America and TWS-related characters. Other Avengers have only really shown up in contexts where Steve or Bucky or other TWS characters are still the primary focus. I'd assume the same would apply to prompts about darker good guys.
Re: On darker characterisation [rape culture tw]
Re the question of what's on-topic: My understanding is that this kinkmeme is primarily for Captain America and TWS-related characters. Other Avengers have only really shown up in contexts where Steve or Bucky or other TWS characters are still the primary focus. I'd assume the same would apply to prompts about darker good guys.