It is simple then Ed, stop making statements such as (quoting you), "It doesn't appear to me Falk ever recovered from the two head blows in the UCLA game and teh CU game back in 2015." ... Instead of pretending, in effect, that you never made them (see above). It is far better to concede error or overstatement, as it shows honesty and candor.
As for CTE, it doesn't present itself on the field of play (which is what we are talking about), but years later. Webster, Aikman and Seau had Hall of fame careers despite it. The alarm with it, is that it isn't noticable until it is way too late. Next, stop conflating CTE, with brain injury in general. We have been studying the effects of brain injury since Phineas Gage. We have come to understand a great deal in the 169 years since. There's a battery of psychometric and neurolodic tests to assess brain performance and decline, to the mili-second, even autonomic response. Assuming that Falk was testing after UCLA in 2015, and his brain performance is now in decline, he and Leach would know it by now, and he would be announcing his retirement. Just because the NFL and the NCAA acted selfishly in the past, doesn't mean the science wasn't there.
We also know a great deal about anxiety. It can cause a brain that has never suffered a injury to shake, hesitate or freeze. Race car drivers, pitchers, surgeons, announcers, have all suffered the yips because of it. Even subclinical issues, i.e. confidence, can play a huge part. Leaf and Gesser demonstrated supreme confidence at this level, but were a shell of themselves at the next. Bledsoe, lacked it, then gained it, then lost it again. Did you seen the difference in Rosen's play against A&M in the 4th quarter?
The "game manager" hypothesis could also apply. Last year we did beat a lot of cup cakes. But the problem with that is Luke Falk, statistically, is among the Pac-12 QB elite in history. 92 TDs, 11,000 yards and a very good 145.0 career PER. PER is a stat used to detect excellence, and we weren't the only team beating and padding stats on cupcakes. Conversely, it isn't like Falk is playing with the talent Bledsoe, Leaf and Gesser had. Never have we won so much with so little, in my opinion. Leach is a miracle worker, but it is harder to beat teams the bigger, faster and talented they become. Since 1985, how many times have we beaten a good USC or UW team? once each.
Dropping 8 has been done for a decade against the air raid. Playing it tight, is more recent approach, but a rookie came in and figured it out pretty much -- we should have scored TDs on all three OTs, in the area of the field where the raid is at its worst.
All things consider, the evidence points to psychology. The others all have significant evidence against.