So I started rewatching Pacific Rim: Uprising and found out the name of the alien race in that movie... Precursors. That also happens to be the name of the alien race in Subnautica. Then it started clicking. I started counting the similarities between them and found some pretty big ones.
Number 1: Frozen Leviathan and the kaijus
Tell me if you think these two look similar.
They're both two gigantic monsters known to have destructive power. Subnautica came out a year after the first Pacific Rim movie, back in 2014. It wouldn't be surprising if the devs took inspiration from the Otachi kaiju and others to make the frozen leviathan. Or maybe it might be a kaiju, as well.
Number 2: Precursors
Both versions of the precursor race have made sentient monsters with peculiar abilities. Granted they don't look similar enough to say that they are directly related, but we also know from the Pacific Rim movies that they come in many different shapes. Could the precursors in Subnautica be a division of the ones from Pacific Rim that is testing a new bioweapon to make conquering planets easier? Unfortunately we don't have much intel on either of their appearances and home world.
Number 3: PRAWN is a smaller Jaeger model
There isn't much proof of this except for the uses and this is a stretch. The PRAWN is a robotic suit of armor( You know what I mean) that does have the capacity to deal out damage to large hostile creatures using the attachable drills/saws and torpedos. In the first movie, the Crimson Typhoon is known to use a saw as a weapon and other Jaegers use torpedos and rockets as well as their fists, which a PRAWN can also do. We know that you are a human, for the most part, and humans could have made PRAWN suits to fight kaijus if they find them during humanity's expansion. While PRAWNs are used for resource collecting, they are also the only thing in game that can dish out big damage to big things. There's no guns at all.
So this is just a wacky theory and probably isn't true, but it would be interesting if the devs did take inspiration and maybe if this was the truth.