I agree that Nyton might have dropped the ball, but I don't think Blas is looking at it the right way.
Blas, you chose Arethusa. Arethusa had certain qualities - qualities I was betting would eventually become useful. I know you too valued the fact that there would be no nanite assimilation going on with this one; I was fairly sure it was a big selling point for you.
The one time it would've been obviously useful, the fight against NH-18 Kotori for starters, the whole group turned invisible except Tom and Rin, exposing mostly them to harm. Even after the fight started, it was other Daisy power armors whom went to the front and risked damage and a similar fate as Rin.
Meanwhile, Nyton stayed back, and fired his rifle from his safe vantage, and watched others put their lives in dire perils in a situation that had he gone into melee, he would have excelled at. Suffice to say that had everyone in the group cloaked up and had Nyton left himself as visible bait, the fight would have had probably turned out to be very different... and also probably ridiculously easy.
It's not that the way the fight was orchestrated past that initial mistake was bad. The team acted together and ruthlessly suppressed the enemy. That in itself was excellent and everyone involved did very well. It's just a bit unfortunate to see one defensive advantage be untapped when it could've made all the difference at the brief point the NH-18 ambushed and made her 'damage spike'. Dealing with Rin's ailments after the fight was pretty much all you could do given the circumstances (and the other people at risk) so I don't think that was a misstep.
Also, Tom chose not to hide himself. Rin did the same. Rin even was ready to stand in the way of harm should an officer be threatened. Those were all your decisions. I think everyone could agree, if you take a step back, that you kind of reaped what you sowed.
Of course, hindsight is always 20/20 perfect. My point isn't leveling blame. It's showing you what I think went wrong so you can pick up on it in the future. There's more yet to come.
It's tragic and unfortunate, but Rin still turns out having been very heroic for the occasion. If that would be character death material, I wouldn't view it as a bad way to die for a character in SARP. Still, there's a chance Rin might actually still survive her sacrifice, even if it took her out of the action. I think that's a decent enough silver lining considering everything that's happened and your present circumstances.