I would consider DRKs Great Sword specific just because thats what they were pre-XI and it falls in line with our Weapon = Class. Great Swords are a type of sword and would fall under Swordplay. Only logical.

In my scenario:

I'm not using any FFT system so DRK and THM would be unrelated. In Solracht's THM would be a pre-req to unlock DRK. We're both using the same system more or less but with some changes/modifications here and there.

Also the points are Base Class specific so they can be used to acquire other Base Class' abilities as well. Meaning if you maxed out on PLD and decide you wanna play DRK you just take your points and go into that tree.