Having used both and written on this subject many times before....
The disposables edge comes from a wider angle on the blade and is stainless steel. So its cutting action is superb for 4-5 shaves, but having to maintain that angle on a fixed straight razor would take a funky looking straight razor.
Now, two issues with your straight razor that I will take a stab at:
1) It isn't sharp enough for your beard. 10 passes on a pasted strop may have helped out your situation and make the blade feel smoother and cut better. I recieved a few straight razors from honers and although they were shave ready, they just didn't do it for me. After 10 passes on my pasted strop. .50 crom ox, it felt like a different razor and its feel was more in line with my preference. Why: Sometimes there is metal hanging on the fin after a honing and this can creating a slight catch and pull action when shaving, thus it doesn't shave smoothly enough for some people. The pasted strop either realigns these pieces or takes them off.
2) Technique does play an important role in getting a better shave. Shorter strokes in tight areas tend to be more effective than longer strokes. All this takes time and some trial and error.
I hope this helps and good luck!
Pabster