The issue isn't "how do we reverse existing CTE cases in athletes," it's more of a prevention/awareness issue.
People had no clue how bad cigarettes were or how widespread that problem was until the proper research was done. That's what's happening here.
The end results of this will be better head protection, better injury treatment (ie quicker concussion diagnosis and longer recovery time), safer rules and fewer parents putting their kids into contact sports.
So, no, we shouldn't be shocked, but we shouldn't write off what we learn when we have more information available about the long-term effects of recurring head trauma in sports.