Actually, I disagree with this statement, because it conflates UFC and MMA incorrectly.
Unified MMA rules make MMA much safer than boxing. In Boxing, there is a mandatory-8 count rule, which can allow boxer to regain their composure post knockout, which is more dangerous than in MMA, where the ref will stop the fight as soon as the fighter can no longer intelligently defend themselves.
My understanding about CTE, is it's the repeated blows to the head, post concussion that causes brain damage. In the UFC, refs will stop the fight to prevent further trauma. In Boxing, fighters will continue to fight, despite suffering a knock-down.
re: UFC vs MMA:
For the UFC's part, once a fighter has amassed a few knock-out losses, they typically are removed from the promotion.
Outside of the US, the rules and safety for fighters is far more suspect (like classif Saku fights where he is nearly knocked unconscious and is allowed to regain his composure and win.