I'm going to go ahead and say that if Garlic Jr. could just *create* something like this, why and how does he not simply destroy it?
You're talking about consistency, and I'd like to note that at no point do we ever see Garlic Jr. ever actually create the Dead Zone, nor is the method for doing so ever elaborated or expanded upon. It could have taken centuries.
If not for these following facts: the Dead Zone itself is the key to Garlic Jr.'s defeat every ******* time; he survives his fights with Goku and Piccolo only because he's immortal, taking a huge hole to the chest that would have killed him during one of his appearances; and he's never shown actually creating the Dead Zone, merely opening black hole-like portals, which, giving them the benefit of the doubt and assuming they are true black holes--depending on the size of the black hole in question, the tier could be anywhere from 7-C--4-A; in what way does anyone assume this scales to his AP/Durability?
At best, I see Portal Creation, Pocket Reality Manipulation, and possibly Black Hole Creation as possible additions to his profile.
Again, unless you'd like to see Toeiverse Raditz upgraded to Low 2-C...and before you claim "outlier", Adem, I'd like to point out that in both appearances, Garlic Jr. is injured by Goku, and Piccolo, with Piccolo harming him in both instances. Garlic Jr. has two showings. If that is enough to establish "consistency", then why is not applicable to at least Piccolo, who injured Garlic Jr. in both appearances, and whom Goku would then scale to regardless, as would everyone in the Toeiverse from Raditz to Freeza by proxy?