Helldivers 2.
Palworld since it's reveal was labeled as Pokémon with guns on PC, having that tag on your game means people will have the disposition to buy it even if its terrible just to see how bad it is because it was a "punch to Nintendo". At the end of the day the market for the game was very wide between Nintendo lovers and Nintendo haters (trying to teach a "lesson" to "very bad" Nintendo LOL). The game is kind of a base building/survival game with taming so you are putting together two genres that have a history of causing "addiction" in a good way obviously. Streamers did their job showcasing the game, and the youtube add was very persistent at least in my country. Also the early access was very cheap and it got the push of marketing from MS and gamepass. The game had everything in their favor to succeed, it only needed to be not terrible and it isn't.
Helldivers 2 on the other hand was labeled as a "generic shooter from Sony", when your game is a Sony game the internet has to hate it, that's the rule lol and people won't buy it to see how terrible it is, they are going to say it's bad even if ends up being great. It had a price tag not that low, not that high but a price tag in the age of shooter f2p games was for many a signal of a major bust. Sony put almost no money on marketing (they did pay to the biggest shooter streamers so that was actually a good move). If you see all these factors there was no way for the game to sell aprox. 8 millions and dominate PSN and Steam for two months but it did because the game is good and people enjoyed their time and they were vocal about it.
So if we are going to talk about the true big surprise it shouldn't be a contest of big bad company vs pure indie company, it should be about everything around each product. From general players perception pre release to the fact that Helldivers 2 was twice more expensive than Palworld.