By the way, I had a witch with a 24 int at level 6.
I started with a 20, got a +1 from levels, got another +1 for being shadow lodge and playing a specific module (you probably know the one), and finally got a +2 int item.
At level 8 or 9, I totally expect to get 27.
As a witch, all you generally do requires your int.
I don't buy that they're overpowered, though, as I've found so many occasions where my slumber hex was unusable for one reason or another. I enjoyed a few levels of being very useful at level 1, but once I hit level 4-5 or so, everything was either immune or had a high save, clustered so that if I sleep the boss his minions would wake him, or positioned so that he ended up waking up before people could finish him off.
My goal was not to provide a coup de grace, but it was my first character and I thought a non-lethal fight winner was something that completely fit into the Pathfinder Society's modus operandi. Since that point, I've seen far more low charisma, low intelligence barbarians than anything else.
Every one of those barbarians needs to roll low single digits to hit, and on average, outright kill the enemy. (or make it so damaged that a single hit from one of the lower damage party members guarantees the death).
Having GM'd for a few dozen groups, I really don't think the witch is any different than about 1/2 of everyone else out there with an optimized character from any other class.