GlassJaw
Hero
Because it's a fill sized sword and it makes zero sense that it should be SA capable when a club isnt. Moreover, the rapier is already to blame for a lot of STR dumping anyway because it's a d8 and finesse.
It only "makes zero sense" if you are bringing a preconceived notion about the narrative of what sneak attack actually is.
If a mercenary class had an ability called "Bypass Defense" or a Thug class had "Dirty Hit", or the history behind backstab/sneak attack didn't exist, I guarantee there wouldn't be an issue.