There are more potential unique combinations of neurons in the human brain than there are particles in the observable universe. What we "know" about the brain is pretty limited. If we use the analogy of energy usage technology we are just now getting to the stage when we are using a bow drill to make fire.
There are squared away neuroscience professionals that don't even believe there is enough scientific evidence to believe CTE is a legitimate disease:
Chronic traumatic encephalopathy is not a real disease
You've got to have academic credentials to get access to his recent full peer reviewed paper, but the authors have been working in the field for some time. Here's a summary of some of his earlier work:
Do sports concussions really cause chronic traumatic encephalopathy?
The problems with the claims for CTE are legion. The samples are non-random - meaning the only times we've seen the determination that it is CTE is when families have detected neurological symptoms. Most of the media you see about this takes those numbers and applies it to the whole population of players - which we have absolutely no scientific reason for doing.
Similar to the "punch drunk" syndrome scare among boxers in the early part of the last century there are legion of things that can cause the described symptoms including alcohol and drug abuse not to mention prolonged periods of undiagnosed VD that is likely not revealed by the individuals to family members and friends and not treated by team doctors. I'm not saying you don't get TBIs from contact sports, clearly it happens. I'm saying that you can't link TBIs to the symptoms described as CTE, at least not yet the way the media portrays it as "settled science."