In your previous post, you were comparing the thief's Weapon Finesse bonus to the slayer's Dex bonus to damage, and asserting that the former would exceed the latter. Acting on your comparison, I pointed out the erorr of not factoring in that the slayer's bonus also ramped. Now you are throwing in the sneak attack damage, which pads the numbers back into the thief's favor. The reason no to do so is that you are combining uncondiitonal damage with conditional damage.
I don't think that's a fair claim at all. The Slayer's Dex bonus to damage
is his striker damage bonus, which is equivalent to the Thief's Sneak Attack. Sneak Attack tends to give a higher damage boost than most strikers get - and it is conditional, but nonetheless can be expected to be available the vast majority of the time.
The entire reason why Thieves are restricted to smaller weapons, mechanically, is because of the high damage of sneak attack.
I mean, yes, this is a slight tangent for the thread - you wanted to know how a rogue can get around their weapon restriction. In the course of that discussion, it seemed that you felt these weapon restrictions were unfair, so people have tried to explain why the restrictions exist.
I suspect they are balanced, which is why I replied to MrMyth that there isn't much problem in allowing the rogue more expansive weapon options at the expense the circumstanstial damage bonus when having CA.
I think the point is that they are balanced as they current exist. Removing the thief's weapon restrictions would lead to becoming unbalanced. I think you may be underestimating how often CA is available - even for standard Rogues, you could expect to have it most of the time, and I think Thieves can expect it virtually all day long due to their tricks - with the only exception being, perhaps, when they are dazed.
Would giving Thieves access to Fullblades break the game? Probably not. There are plenty of levels of optimization already out there, and many other worse combos.
But it would, at its core, give the class a higher damage boost than is appropriate for the general game. A Slayer's damage bonus is significantly less than a Thief's. He has less options available to expand his damage. Giving him yet another feat that can increase his damage by 4 points or more... well, it starts to get unreasonable.
Now, its fine if you want to find a way around this for thematic reasons. And... several have been suggested, whether reflavoring or talking with the DM or otherwise. But mechanically, yes, there is a good reason for the Thief's weapon limitations - and while some folks may have been rather extreme in their defense of this fact, it doesn't change the truth of what they've been saying.