I think you need to accept that post numbers are a preference since they provide a useful function, so if the lack of them doesn't bother you, then feel free to use forum software that doesn't have them, but don't try to convince me that it's somehow better for it, because it simply isn't.
Oh, I clearly understand they are a personal preference, and not trying to convince you to change that... but they
are a preference that serves no technical useful purpose as a reliable reference point once posts start getting deleted and especially if they are used as reference for people to retrieve content from earlier posts. Those references to post numbers no longer are valid whereas a link to the post itself is unless said post is deleted that is referenced.
That is the point I am making. Unless you never delete messages ever, they are subject to becoming incorrect reference points.
As I have commented, I simply cannot find a good technical reason for use of post number other than "that's what I've been used to and what I want" or "it makes it easy for me to figure out how many posts are in a thread instead of doing quick math". And that's fine and a valid reason for that individual.
But I'm pretty sure if you took a poll of admins and forum users, the majority of them do not even pay any attention to the post number on the side of a post, other than maybe to see the last number to see how many threads in an area (which again, most everyday users aren't going to really care about, only being concerned that they are on the last post).
And I'm looking at it from the aspect of an admin for what helps the users. Having a post referring a user (or users) to incorrect post numbers does nobody any good, and that has historically been what post numbers on the side of a post have been used for.... all the way back to the era of the BBS. QuickBBS, RemoteAccess and Maximus BBS all used post numbers. I honestly don't remember if they also had the same issue (I think they did, but that has been a "few" years ago since I ran my multi-node BBS rig).
Being able to click on a a hyperlink to the actual post referenced is much more efficient, especially if a thread is long and the referenced post is 3-4 pages back, than going backwards through pages looking for a post number.
As for a normal user, I seriously doubt they come back to a thread a week later saying "well, I left off with post #8 so now I need to read #9".
So, from a technical standpoint, I can easily see how developers might choose to do away with them and push the use of a reliable method of referencing other posts. The loss of them apparently did not kill Invisions ability to work.
It is ultimately what you are used to and whether you prefer a quick and effective method of referencing other posts. As for finding them for use as a personal reference point, unless you are making a note of the post number to get you in the general area, a bookmark function will continue to work better generally.
Now, if you are getting the link from the post number to use to bookmark from... the
share
button does the same thing, and does it easier/friendlier.
Now, you reference PM threads... I wish bookmarks worked on them. I'm sure there is yet one more add-on (and probably a paid one) that can be used for that.