Jyothida shastram is blessing from god. it is very accurate. If in the panchagam, it is said that the sun is in this rasi, as per nasa calculation it is there too.
based on such accuracy loong time ago, it is indeed safe to conclude only rishis were able to come up with the shastram based on the star location.
even ancient time, if the stars were not right, time is said to be bad. thats why even now, english words such as as catestropher and disaster , the root word is aster(star). all is based on the star.
of course, all the stars listen to god's direction to save the dharma.
A devotee of god don't have to be tormonted for any evil effect of the star.
THus in kandar shasthi kavasam, it is said," navakol makilunthu nanmaiye seiyum'.
In thevaram it is said similar in the thirukolaru pathigam too.
JYOTHIDAM is very accurate, but the instruments who are the astrologers are not necessary good eough to utilise the power of it.
To understand more about how the system works, i give two links for your reference.