It's an especially weird complaint to make given that Tarkovsky's version also missed the point of the original by focusing on the humans instead of the planet. And was also criticized for it by Lem. Additional source.

But then again I have come to accept that redditors only care about faithfulness to the source material when it's source material they personally care about.

If they don't care about the source material, they're all "But adaptions don't have to be faithful". When they do care about the source material they go "how could they possibly miss the point! Why did they think they were so much smarter than the original writers?".