Very compelling arguments and nice piece of detective work. What is interesting is how this never got corrected by checking back at the original source.it is as if a satellite get ejected from the mothership and finds it own orbit and stays put.
One reason could be the historical events and timeline- as time went by the Greek dominance waned and Chandragupta had taken back the territories lost to Greek. Over periods of time with the tropical- sidereal variation increasing- things would have been in flux anyway.
There was no reference- sidereally- left to calibrate with.
Traditionally, even now, there is a gradation in Brahminaical professional- those earning money by Fortune telling or performing rituals and accepting dakṣiṇ?? are not par with the teachers,scholars and vaidyas.
If the scholars became patriotic then the general public only needed the astrologer for festivals and electional astrology( marriage,house warming etc).
PD
'A Note on the Indian Planetary Exaltations and their Greek-Language Sources'.