The sting ray can be very helpful for taking out fly fish be careful when you use it.

Any advice for using the Splat Charger?
That seems like a huge curse whenever I get it.

Pray you don't get one.
I hope we will be able to pick our own weapons someday in the future.

I haven't played too much of Salmon run, but I have a question. How do the rank ups work in relation to the gameplay? I definitely noticed that it got harder after getting the first promotion. Is there an even harder version after that? How many ranks are there?

I am not sure how many ranks there are, but stuff gets super hard.
We have already talked about Motherships and searching for Goldies but there is more than that.
The tide shifts and the basket moves locations, you get to use cannons to take down massive hords of Salmonids.
Sometimes there is fog and othertimes hords of glowing eyed Salmonids will flood the screen.

Currently I am at Overachiver 80/99, I would be much higher but most times I go to play...
I am not able to.

I don't even mind the mandatory weapons that much because they add variety and ensures there are different roles (aka what if a there are a bunch of rollers), but the Charger is so incredibly useless that it really makes the person who is using it dead weight.

I'd be fine if they just rotate it out forever.

I want the ability to own my gear, and for that gear to be able to level up.
That would give Salmon Run its own progression cycle.
A game within a game.

And with that, Salmon Run is closed for today.

Dam.

I think that as the game sells better and more and more people play it, they will eventually leave Salmon Run permanently open.

That too is my theory.
 And oh boy, they better.