I don’t think parent commenter says so, he only claims one thing for himself, that pardon power is always a miscarriage of justice. Then he asks another thing of us, which is explicitly excluding himself, indicating that he thinks all laws and all applications of law and justice is fair.
We will always find ourselves in situations in which our existing laws allow for people to fall through cracks. I can see pardoning as a way to address that partially, yet it doesn’t explain what an adequate judgment would be instead. It’s simultaneously important in niche situations and yet too coarse of a solution.