I finally got a chance to go and watch the original video (which necessitated looking up "G6" and led me on a brief Wikipedia tour) and then the other two.
I think there are good things about the Quidditch one--the Quidditch/G6/"fly" connection you mentioned, the more-direct copying of the style of the original video--but I'm surprised to see a suggestion that Like It's Quidditch is more lyrically sophisticated than Roll a D6.
Roll a D6 does several nice things with lyrics. For example, they vary the rhyme with "wizard" from verse to verse, unlike the original song, making it less boringly repetitive than the original.
Meanwhile, Like It's Quidditch starts out with a lyrical problem: Quidditch doesn't, in fact, rhyme with G6, both because the stress pattern is wrong (first syllable vs second) and because "itch" and "six" don't rhyme. Near enough for hip-hop, sure, but then they go and compound the problem by trying to rhyme "figures" with "wizard." I think that might be more or less within the bounds of rap rhymes (where the vowel sounds seem to be more important than the consonants), but even getting that close requires a stretch (how many people associate "figures" with HP?).
And in Roll a D6, I laughed out loud at the clever reworking of "put yo hands up" to "raise them up" in reference to a necromancer raising the dead.
And even though the video for Roll a D6 doesn't echo the original very much, it's got surprisingly high production values.
Anyway, so not only do I agree with you that Roll a D6 is a better parody on all sorts of levels, I also claim that it's got cleverer and better-constructed lyrics.