Tua is also extremely unlucky then most other mobile QB's who looked outstanding for several seasons and helped their teams win until injuries that werent concussions but knee, leg or ACL injuries forced them to alter their playing style to a more pocket-passing oriented system. Past QB's who fit this mold were Randall Cunningham, especially Michael Vick post-Falcons, Eagles tenure from 2009-2013, Steve Young was essentially forced into retirement due to concussions suffered from late hits, including one that knocked him out on the field vs. Cardinals in a early 1999 MNF game. Their are some, albeit relatively few, mobile QB's that do defy the law of averages and manage to avoid serious injuries, or at least, career-threatening ones.
Those above-mentioned guys either played in an era where they were lucky or fortunate enough not to receive as many concussions in a short period of time like Tua or more accurately, 20-25 years ago, NFL's concern for player safety as it related to effects of concussions wasnt a high priority and most trainers just made concussed players sit on the bench for a quarter or two "until the cobwebs cleared up" and then sent back out again.