Here's another:
We think the main story of Splat 3 was the weakest in the series.
-Why did a... Sentient, giant, grizzly teddy bear...steal an old man and try to cover the world in goo?
-Why was Deep Cut even there? The story probably wouldn't sound any different if they weren't.
-Why are Callie and Marie so chill about their grandfather's kidnapping/dried out state??
-Why is Lil' buddy even here??? (We love him, but still.)
As a certified Return of the Mammalians enjoyer, I can't disagree with you. Side Order has its flaws, but it's at least consistent with its overarching theme of Order. Return of the Mammalians is only chaotic in that many elements feel slapped in for the heck of it. If we wanted Deep Cut, they should have been the center of attention instead of wet Team Rocket. Even if the New New Squidbeak Splatoon was inevitable, they could have at least thought out a conflict instead of shoehorning one in. Mr. Grizz's motivations are unclear and also inconsistent with his previous characterization revolving around corporate greed.
I also believe ORCA and the fundamental premise of Alterna were spectacularly wasted. The idea of the last human settlement have so much potential to be literally anything other than a lore dump unlocked by completing levels. That's what Sunken Scrolls were for, and we got those too. And the implications??? I know the NSS (and probably the NNSS by extension) conduct their business in secret, but an archaeological discovery like that would change the world!
Oh, and Li'l Buddy deserved more than one scroll worth of backstory. At least it gives me room to make mine whatever I want him to be.