So no one has gone with Halberd, Pollarm Master, Great Weapon Master, with a dip into fighter for great weapon fighting? You now have two attacks -5 to hit +10 to damage and you reroll 1s and 2s for the sneak attack dice. Variant Human allows this at 5th level.
Well, it isn't really a "dip" if you are getting two attacks unless you just mean the reaction attack from PAM. Most of the time, you'll only be getting one attack per turn. To maximize the odds of landing the sneak attack, many rogues use two-weapon fighting for this reason and it is why no rogue subclass gets Extra Attack.
Also, even on the d6's, the GWF style raises your average from 3.5 to 4.167, or 2/3 a point per die. Even with a 10d6 sneak attack this is only 6.67 damage. And most rogues generally won't get above 5d6, so you are only talking 3, maybe 4, points of damage gained.
Now, unless you have advantage, the -5 to attack also means you will miss your sneak attacks more than the +10 benefit is worth.
While it might seem like a potent combination, it isn't really that effective and you are doing it at the expense of two feats and a fighter level. Also, at 5th level, that fighter dip is costing you a d6 of sneak attack, about 2 points of damage typically, making the GWF style even less impactful.
