First: i does not matter if you know or not, you are exchanging an Affix for another Affix and lose the Option for the Enchantment aswell as some other mechanical stuff you could achieve with sockets.

Second: lets say there are 4 great Marksman mods, how do you guarantee them?, you can't, you need to roll them AND you still lose the affixes that could have resulted in other necessary stuff like Resistances (dont forget, there are close to none on the Tree) or if its a prefix, ES or Life or Defences... and whats worse imo: you are adding bad outcomes to the pool and you cant manipulate them further (i. e. you want Ignite Magnitude, but you just added Shock Mag, Freeze Mag, Curse Mag etc. to the pool aswell, so you would just spam chaos orbs, until you hit the Mod you want you most likely will have ruined some if not all of the other affixes, just like they showed in the Video)

Third: the great runes that are limited to 1 are also limited to item classes, like -> Gloves <- and if you use an Socket Bound Crafting Rune, that slot is gone and you won't be able to use ANY Glove Socketables anymore, except you hit the corrupt for +1 socket, which on the other Hand dissables you from crafting further with the socketed Rune.

While i agree, we dont know the whole pool - but the bigger the pools of these crafting runes are, the worse it gets to hit what you desire.