In git (and hg), you can use force-push to delete the commit, but there are risks.
In all VCSs, you can create a "revert commit" - using git revert or equivalent - which just un-does the changes in a new commit (leaving the thing in the history).
Yes, I mean the way it works in Meta's Phabricator: it runs the equivalent of git revert + git push behind the scenes.
Given lack of land integration in Phorge, it sounds like that could be an arc command. arc unland D12345 could find the related revision and automate the revert.
The expectation from arc land is that it pushes the change. So, if we go the git revert + arc diff route, which requires approval/landing, I think it would be more semantically correct to call it arc revert or something similar, as 'unland' would be expected to also push the revert.