OK, let's say hypothetically, that soft-delete hides the post into a single barely-one-line-high message in place of the actual content, simply to say 'This post was deleted by a moderator', and that for those who can see it, there's an additional link 'To view this message, click here'.
We're only consuming a small amount of space on the screen but we're providing context.
For example, consider the following thread:
Post 1: <says something interesting>
Post 2: <blatant insult>
Post 3: The post above me is rubbish.
Now delete post 2. In the classic context you're left with:
Post 1: <says something interesting>
Post 3: The post above me is rubbish.
Which artificially distorts the meaning behind it, though unintentionally. Perhaps there's education that Post 3's author should be more specific, but whatever, it's caused more than one row that I've seen on sm.org, let alone elsewhere.
Under what I'm suggesting you'd have:
Post 1: <says something interesting>
-- this post has been deleted by a moderator --
Post 3: The post above me is rubbish.
Now, no context is lost. It's quite clear to everyone who can see the thread what happened. No misunderstanding is made based on anything.
If you really did want to delete it, there should be a permadelete option but in almost every case I've encountered, moderators can all only soft-delete and only admins can permadelete, so in most cases nothing changes.
The only counter argument that remains as I see it is the fact you have a potential case of 'soft-soft-delete', for which you can then manufacture an argument of 'but I need a soft-soft-soft-delete' ad nauseum. I'm not convinced there needs to be an extra state, nor am I yet convinced that the ability to unapprove a post is required.
If you want to take it out of circulation, soft-delete it, that's what it's there for. You can put it back later if you need to, or you can spirit it away with the caveats of lost context above, but it should be more obvious in this situation.
* Arantor can fully understand where you're coming from, just not convinced that the described workflow is really ideal.