I know nothing, I am just posting old information from memory and trying to clarify some things.
Charms: Originally there were only Magical Charms and for a charm to drop from a monster, a drop table is considered for the affix level based on your character level and the monster level, thus, certain monsters may drop a Grand Charm, however because of your character level and the monster level it will NEVER be a +Skill charm ... best example a +1 Fire Skill Grand Charm with +45 Maximum Life can only be dropped by x# Monster Level, say Hell Diablo or Hell Baal ... hence those used to be kept and re-rolled ... item level 99 if I recall.
Introduction of Anni and Torch ... specific monster(s) need to be killed to get those charms, however Gheeds is also based on mlvl in Hell difficulty. Keys & Orgains are monster specific and hell difficulty, doesn't matter what character level is ... funny that.
So, for Sundars Grand charms, it is different again, most likely (guessing) based on character level, monster level and because you have a 50% chance of the Grand Charm being Magical or Sundars ... now that is just a guess, but think about it... there are no such thing as Rare or Set, or Unique (outside of monster specific) Grand charms... thus a higher % chance to find Sundars.
Runes are from the monster drop table, magic find has ZERO(0) effect, they are just random ... RNG ... example, I found a Ber from a normal monster in Hell Tristram (okay, this was D2LoD back in the day) ... that was luck and RNG.
Here is an assumption with Terror Zones, monster level, character level, monster drop table has Elite item drop sequence more often than other monsters (note, I forgot to mention that Elite items are removed from monster drop tables if they are not the right level, same as character level) ... so, in TZones, more chances to have an Elite item drop from the monsters drop table, and RNG rolls either Normal, Magical, Rare, Set (if it can be a set item) and Unique (if it can be Unique) will appear.
All this means is that it is RNG, maybe you do have a slight advantage in finding items in TZones because Elite base items drop more frequently than the other monsters in the game.
Oh, as for the video clip... yeah that was a waste of my 19 minutes of a person trying to use hours as a measuring tool for drops.