You’ll just start removing the valley entirely unless you carry on as the OP is doing. There’s no ‘clean’ method currently of making a roof valley.
There’s the OP’s method, which has the jagged edge problem;
There’s the sloped valley method, but you’ll end up with a large flat surface and remove the valley entirely;
Same thing with iron and gold, @Cookviper;
You could step the roof. It won’t look as nice close up, but from afar it’ll look fine;
Or go full Minecraft and just go the voxel route;
Like I said - there are no clean methods, but plenty of work arounds. It really depends how close people will be getting to said roof. A lot of these methods will suffice for the bigger picture, but if you’re pedantic - like me - then it’ll always irk you.