I don’t know diddly about the details of vBulletin
But I’d imagine it comes with instructions on how to set up its database. Including which indexes will help the queries it uses. It’s pretty much the market leader in this now-obsolete category. Even back when the category was big, they were biggest. Seems pretty obvious that database tuning for this app would not be something that takes creativity and deep expertise; more like RTFM.
And it’s a reasonable assumption that the folks over the years who’ve set this thing up and done the maintenance and the several server moves and such did indeed, at least a few times, actually RTFM.