The hex bar gives the user a very different leverage and handgrip. It is much easier. Not to say that using it cannot improve your overall "normal" deadlift. But it like "sumo" is more of a specialty lift in my experiences. Changes the ROM and the movement altogether.
What I have learned from my years, and especially true for strongman or PL, is that if you want to get stronger in one specific lift, you need to focus on that lift, and multiple times per week and you want to use secondary or assistance lifts, to supplement strength for precisely that specific lift.
Case in point, I can take a 200lb kid and work with him only on Atlas Stones for a year. And he will be throwing 300+ over a bar. I can take the next 200lb kid and have him do a variety of gym lifts, deadlift, bench, etc. I can have him benching 300, squatting 400, deadlifting 500. And I can take him to that 300lb atlas stone and he will be lucky to get that stone 6" off the ground.
The other kid that does the stones won't be benching probably anything but maybe 225.
It's all relative. Certainly your basic lifter with experience, generally speaking will have an advantage but I have learned that if you want to get stronger in a specific lift, the best thing you can do is just increase intensity an volume..on that same lift.