For very shallow curves like this, you need to improve the adhesion of the outermost perimeter to the perimeter immediately inside it. There are a few things you can try to do this....
Firstly, ensure you have a filament cooling fan fitted and its ducting pointed to maximise airflow onto the just-extruded filament. Set the fan at 100% (you have it at 60%..not sure if all cooling fans allow fine speed control). You want to hit the filament with as much cool air as possible to harden it to stop it wilting!
Secondly, slow the perimeter printing down ( say to 40%) and increase the extrusion multiplier. I'd consider using a second process for this....set the extrusion width to manual and wind the multiplier up to say 1.00. This will push more plastic out without the extruded lines being shifted further apart...this should force better adhesion.
Thirdly, I'd try thinner layers...again possibly in a separate process. This will reduce the overhang slightly.
Finally, despite your doubts, I'd add an extra perimeter....just to give a little more support.
Of course, one thing I can't do and have no experience of using is a dissolvable support material.....but I imagine if using , you simply get support gaps and separation to zero.....and don't end up with unsupported extrusions.