The Send Approval Email action is an implementation of the actionable messages framework. This action aims to simplify approval workflows without having to implement a custom service. And like you've observed, there are some limitations to it
You are not able to get the email address of the person that "Approved" or "Rejected"?
I believe this is supported by the actionable messages framework but is likely not exposed in the action. Please feel free to raise a feature request to include support for this.
You are not able to get the email body of the reply email to see if they typed anything in or no way of getting custom comments?
Currently, you get a simple case with buttons to record a response. While you could include a comment box using the actionable messages framework, it's not part of the Logic Apps implementation. Again, please feel free to open a feature request to include support for customizing the action message.
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Since the above limitations are still possible with the actionable messages framework, you could have your own custom implementation that you could trigger using the HTTP WebHook Action (which is very similar to how the official action works).