In my opinion, r= 0.7R must be close enough to the truth, when the chord is constant
My calculation for an ELA (8.28 x 0.22 m, aerod pitch 2.8°) at 450 kg and 120 km/h and sea level gives:
A.o.A disc = 9°
a0 = 2,8°
a1 = 2,15°
b1 = 1,06°
It takes into account the non-uniformity of the induced speed.
It is difficult to know the actual pitch of the blades in flight, because of the possible twisting .
However, your angle of attack of the disc seems to me very underestimated. This would imply an exceptional L/D ratio of 11.9, only believable at mu of 0.35
Are you sure it is not the angle of the shaft?
For my calculations I assume cD0 = 0.011
So, at 1000 m above sea level, 390 kg, and dia. 8.5 m, I obtains 7.6° (disc) or 7.6° - a1° = 4.6° (shaft)
L/D of our modern rotors is better that 7, due to the high aspect ratio of the blades. L/D max = 11 about (ELA, MTO, Magni's rotor alone)
Value 16 calculated by Dudda is unfortunately unrealistic due to assumed Cd0 (too low)