Next thing - your elbow/forearm aren't resting on the body of the guitar - it looks as if for the most part they're floating in mid air so with that instability (do you rest on the inside of your forearm? hard to tell) to contend with it seems to be contributing to the excessive reliance on the side of the thumb for stability as well as muting. Playing in a classical position is absolutely fine, just check out the position of your elblow/forearm relative to the guitar (for comparison - that video of Guthrie and yours).
From your last thread Mr 777 - I was right
Can you adjust to a 7 now you've noticed that?
While raping a bear in Yellowstone and snorting coke out of a freshly-dead baby's skull, I finally felt that I had found my calling and built a time machine out of Iraqi WMDs and LOTS OF HEMP WHOA. Using this time machine I went back in time and shot JFK from outer ....ing space. I am now your god - Jeff
.....and then all of a sudden he drops the musical equivilant of a steaming turd right in our laps - ESP Griffyn