The original chess game with the important changes wrought 1492-1851 is best.
This means that there were changes. And not only minor changes but Important ones.
Why? Because chess needed to be tailored to the needs of a new era, it needed to be made faster.
This did not ruin or deny 'shatranj' in any way. Just improved on it.
Playing on a bigger board would not ruin or deny chess just tailor it to the needs created by the new age of databases and engines.
The major changes:
The bishop can move further than the original elephant
The queen is vastly more powerful than the original advisor
Pawns can now move two squares when they start their journey, and consequently en passant became necessary.
Castling has replaced the king's leap.
White always moves first; the queens start on their own color; there must be a white square on the right of each player.
In medieval Europe a gradual revolution took place ( which ultimately for a certain period made Europe the greatest and most innovative power on Earth ) which brought with it the acceleration of life in general. It is natural that this new era called for the speeding up of chess which was deemed to be too slow.