The Blaster Edge is kind of a stupid weapon. I'll grant that. But Fujin's chakram is also a stupid weapon, as are Kiros's katals and the concept of a gunblade. Criticising Rinoa on her choice of weapon seems odd when there are way worse things to focus on.
Angelo does a double backflip to return to Rinoa after causing an explosions and damaging enemies. I highly doubt she is in any danger of being hurt; the only "animal" violence is conducted against Moombas and monsters.
Blaming the writers is just about all you can do. Who else are you going to blame? The writers made her that way. The fact that we found her to be stupid and childish is highly likely to be deliberate, and still fits within her (attempted) development. She's a spoilt brat, and is told as much by Quistis. She is not a trained professional mercenary. She has abandonment issues because her dad was never home and her mother died. She spent most of her life in a gigantic smurfing mansion, and then joined a troutty little resistance group that doesn't actively fight, where she is known as "the princess."
She is supposed to be like this. You say "common sense" but the adage is that common sense isn't common, and everybody is an idiot. People don't always make logical decisions, especially under pressure, especially when emotional, especially when they feel left out, and especially when they have something to prove. Rinoa thought she had a good plan, thought she had an avenue to work, and thought the party wasn't listening to her. If I were her, I would have tried to take Odine's Bangle to her too. There's no logical reason it wouldn't work.
You're not allowed to bring in the worst plot point in the entire game as evidence against Rinoa too, by the way The convenient amnesia trope doesn't include her. And even though it feels incredibly weak, it still fits. It's not illogical. There's an element of story-gameplay segregation, and it's hard get a grasp on Irvine's reactions 'cause they're not quite lining up with what he says later, but it's still not so much a hole as it is a hilarious asspull.
"Convenient to the plot" will, you'll find, explain a lot of things in a lot of mediums incl. tv, movies, games, and books. People bring up the Eagles from LotR - why didn't they just fly to Morder and drop off the ring and evil would be vanquished? Well, that would be one hell of a short book (mind you, Tolkien would find a way to flesh it out, and Peter Jackson would still make a trilogy of films about it). The fact that Sephiroth only starts putting his plan into motion when the party are able to stop him is super convenient too; had he started earlier, or later, and not precisely when Cloud and co. entered Shinra HQ, he would have succeeded unhindered.
Your last point sticks. Rinoa succeeds at opening Squall up because it was necessary and it was not done in a way that I find believable at all. I cannot believe that Squall developed feelings for her at the drop of the hat, which leaves the only possible explanation as "he would've flipped out over losing anyone under his command/that he's fought so long with" and that I can't see happening either. Squall is a goddamn rock and somehow they made him cry and I didn't think it worked at all, but hey, smurf, it did, so at least we got the rest of the game.
Squall is Dead is an awesome theory.
And lastly, most things are a plot device, it's just about how cleverly disguised they are.