The transcript is interesting. It's long, not because W6 had much to say, but because he was repeatedly asked about what he did and did not observe, with the interviewer returning to the same core questions. It seems a fair and thorough interview to me - no leading questions. The interviewer did not appear to have any biases or agenda, other than probing John's account.
The fact that the scuffle moved a significant distance in a short time, without Trayvon ever losing top position is telling. While John notes he didn't actually observe Trayvon landing blows, Trayvon was well positioned to do so, and the interview doesn't rule out that John's initial impression of "MMA-style punches" (cooraborated by GZ's actual facial injuries) may well have been accurate. The interview also tilts in GZ's favor that GZ was probably the one screaming, with John giving objective reasons why he still thinks it was, even if he didn't see George's lips moving in the dark.
During the time of W6's observations, GZ and TM apparently weren't clumsily "rolling around" as two untrained people scuffling might do. Trayvon would have had to have good balance and positioning to thoroughly dominate as he did. It will be interesting to see if GZ's defense can uncover any further evidence of Trayvon's comfort level with hand to hand combat.