Understood that this is a pretty severe edge-case for a very minor annoyance

1. I merged a longstanding branch which resulted in a merge commit of 512 files (unplanned power of 2, or phab caps at reporting > 512).
2. I used arc diff to create a diff of the merge commit. I needed ~2 others to review certain parts of the merge which I was concerned with, which is why I created a diff.
3. I was presented with a note from arc diff suggesting that large commits are not a good fit for review.
4. Caution to the wind and continue anyways.
5. Update the merge commit with additional changes/fixes.
6. Update the diff with arc diff
7. I was again presented with a note from arc diff suggesting that large commits are not a good fit for review.

This was only a minor annoyance but assuming that the existing diff is already considered sufficiently large, having the warning repeat seemed unnecessary. There may have been a better way to handle review of the large commit to create small diffs of the areas I was concerned with, but I wasn't able to come up with a clean way to accomplish that due to it being a merge.