If the SA damage meant rogue was doing significantly more damage than anyone else when it worked, it might be ok for it to not work so often.
If monsters weren't handed out crit immunity like free lollipops, it might be ok. If Fortification armor wasn't so ludicrously cheap, it might be ok. If even the slightest bit of concealment didn't straight-out deny SAing at all, it might be ok. If getting reliable ranged SA past round 1 was cheap and easy, or if Rogue had the hp, AC, and fort saves of a cleric PRE-buffing to adequately melee with, it might be ok.
...It is not ok.