The reason OG3 is the new captain outside of just having more experience is that they've arguably had more impressive feats. The one that quickly comes to mind is sneaking around and surviving inside the Deep Sea Metro entirely Solo until saving 8. But also something I realized thinking about it a bit, I think they also sorta fought off potentially the strongest version of the Octarian Army. In the base campaign for Splat2 and 3 the Octarian Army's numbers were likely dramatically diminishing thanks to so many trying to reach the surface after 1's final battle.
And for Octo Expansion the Octarians that are there are set up as mindless drones for tests on its subjects not as an actual military and a similar thing for 3's base game as a whole, with those remaining that were kidnapped and just corrupted by the Ooze. And once again story wize by that point there's not that many left compared to how vast the army once was.
Also subjective take but I think 1's campaign was more difficult in general than 2 and 3s base game campaigns too.
And to address the other agents (except Neo3 because they couldn't have been an option given they arrived after 0G3 was already given the title) since people are probably gonna be curious and maybe mad if I don't.
Callie and Marie already have full time jobs as idols that are still going. Neither of them can be Captain cause of their already existing jobs.
4 is great, Side Order deliberately states that 4 is noticably strong which is great. But I can see 4 getting turned down for lack of the experience OG3 had or that Cuttlefish just knows OG3 better given they've seen their feats with his own eyes.
8 I feel like given her primary goal even if she was offered the position she would have turned it down. Due to the circumstances of OE it's kinda obvious she was an honorary/temporary agent anyways plus SO confirms they've been spending most of their time with Pearl and Marina who we know definitely Aren't agents.
Reminder that Neo Agent 3 canonically cannot say anything about the log, meaning that no one else knows anything about how they came to be or the fall of humanity or anything about mr grizz
IM 2 DAYS LATE ON THE ANNIVERSARY BUT YIPPEE HAPPY 6 YEARS SPLATOON 2
Hehe 2 days late. 🤭
Ok but like I've been wanting to draw Sol's picture she has hanging on her wall for a bit. They took a celebratory photo of her getting an apprenticeship with Sheldon. ^^
Bonus:
That precaution? She's gonna train those eyes to stay up and her memory on the amount of info dumping she's about to (and now already) receive(s).