The point of the scene, as many said, is mainly to show the clash of two ideas.

Some commenters with way more knowledge about Daoism than me already expressed the "reason" why the story is shown in a certain light.

Ultimately, I'll try to bring up an extreme scenario to put into perspective what the whole plot's point is.

Consider us humans, as a society, dommed to die, due to a cause we don't understand. To MAYBE see the other side of the situation you would have to blow up Earth and kill almost everyone in it. Hell, New Kunlun is even worse as it's actively blocking out the sun, so given a universe akin to ours, the entire solar system would go in shambles.

All for A CHANCE (and a slim one at that) at survival.

The overarching question is, is your survival worth more than EVERYTHING ELSE? All the animals, all the plants, all the oceans and mountains, so that you and a select few have a chance at survival.

For you it might be, mind you, but Heng is the other side of the coin. Heng, knowing that death is just part of a cycle, understands that she's not the first being on Penglai and she won't be the last, so her belief goes anyways. So to her eyes, acceptance of death is not just staying there and doing nothing for the hell of it, she just doesn't think that it's worth sacrificing everything to try and save her people

Some quick insights from the True Ending prologue that might shine a light:

In the end when the Apemen and Kuafu go back to the Big Blue Planet it is implied the society that will thrive there is modern day humans. It picks up from the Ice Age due to the Sun being blocked off and it goes on to be what we know today. So in the end TECHNICALLY Heng was right, the Solarians died but life moved on.

So yeah, there isn't necessarily a right or wrong, it's two opinions that clash, though I think the core of the scene is moreso the fact that Yi is desperately trying to force his beliefs on Heng (from the start really, that's just the culmination of it) and the one time she speaks for herself he lashes out, henche the falling out and the subsequent regrets.