Here is a diagram to demonstrate how impossible it is to run at full speed and throw the ball so it is not going forward.
(Not sure if the image is working. The sine of the angle that a ball is passed at multiplied by the speed of the pass, has to equal the player's forward running speed for the ball to not go forward).
I did some rough timing from the Eels match, when Jennings made the break leading to the first Eels try (ironically disputed by Roosters fans for a forward pass).
He was running at about 8 metres/second.
I timed some passes as well. A regular pass seems to be passed at about 10 metres per second.
So Jennings would have to pass the ball back at an angle of (Theta = sin^-1 8/10) 53 degrees for it to not travel forward.
To give you an idea of how ridiculous an angle that is if we required it from a team, if the players were spread the width of the field, and the far winger was in their corner, and the ball was played on the opposite edge, it would have to be played 90 metres in front of the far winger for the team to maintain that angle (68 metres times tan 53 degrees).
So those who want all passes ruled forward if the ball travels forward, to run at good speed and "compensate" with a deep backline, the backline has to be set 90 metres deep. Or play has to not go the width of the field, or players have to not be running fast when passing. Any of those is patently ridiculous (players not running when passing, not using the width of the field for a passing play, or setting the attacking line 90 metres deep) and would ruin the game as we know it.
If you are arguing anything other than the rule as it is, you clearly are just being obtuse or wilfully ignorant.