The writers get around this by having him send back the samples in probes so that he can physically go save the rock alien.

That's a bit disingenuous. Unless the movie didn't bother to mention that it was supposed to be a suicide mission in the first place and the multiple probes were the only plan to get the information back to Earth anyway.

The alien was the reason why he even had the option to go back to Earth in the first place. Also without the alien he would've never solved the mystery of the space goo. So he didn't choose to save the alien instead of his own species he chose to save the alien instead of going home. Because getting home alive was a long shot anyway.

Anyway Project Hail Mary is just The Martian 2. The main character is Mark Watney with a different name and backstory and the alien is just the alien version of Mark Watney. The plot structure is pretty much exactly the same too. And not just in the most basic sense.