Not everyone is affected the same by the same injuries. Why do some people get dementia and others don't? Why do some people get cancer and others don't? Just because you or Aikman don't appear to have it isn't a valid presentation for it's existence or non-existence. I'm not even saying he has it...just suggesting it as a possibility due to the downward spiral we've seen. Other players who had that downward spiral and died were later found to have it.
But there are examples out there of even mild concussions slightly changing someone's personality. Other things can do that too, like drug use, alcohol, etc. You don't even need CTE for that to happen.
The bottom line is...some dudes go through childhood and early adulthood with no trouble, play football, and suddenly they're a slightly different person, getting into trouble, etc. It's certainly something to look at.