Are you talking about deleted post that are removed from the data base, deleted posts that are only visible to users allowed to see deleted posts or a post deleted by a user that is still visible as “(Post deleted by author)”?
In the last case the user could still restore their post after posting it a second time. That would render this measure against double posts ineffective.
I have also expirienced that I accidentially posted in the wrong topic, deleted my post and had to wait a few minutes before I was allowed to post it again. By default unique post min is set to 5 minutes. I think that’s an acceptable waiting time to benefit from a spam-free forum.