Helldivers 2 isn’t a game made by a first party, if I remember correctly. Not quite the same situation.
Helldivers 2 is a first party game in PS, and 3rd party in Steam.
As you can see in their game credits, in AAA games the lead dev studio provides only around 10% of less of the total amount of people who works in a game. The rest are from the Sony, either from the publishing, editorial and corporate side, or from internal or extearnal support/outsourcing teams funded and managed by Sony.
That approximated percentage applies to 1st, 2nd and 3rd party AAA games. So in Sony's first party games there's not much difference if the lead dev team is owned by them or not.
Specifically, Helldivers 2 is a second party game in PS. Which means it's a first party game (1st party game = it's published by the platform holder) that had a 3rd party lead dev studio (3rd party studio = not owned by the platform holder).
3rd party games are the ones published by a company not owned by the platform holder. 3rd party publisher = publisher not owned by the platform holder.