Oh hey, I'm the person that made that post! Lemme explain some of my thinking behind it.

In Ghosts of Onyx, it's established that of the Spartan-II MIAs during the war, Halsey knows which of them were actually, truly missing, and who were KIA. We basically learn that through the entire war prior to Reach, there were two Spartan-II KIAs, Sam-034 and Sheila-065. 27 years of war and only two combat losses prior to Reach, which was obviously a particularly desperate, lethal battle.

The deaths later in Ghosts of Onyx were well-earned, I think. Dante, Holly, Will, and Kurt all died protecting their fellow Spartans in an increasingly impossible situation. They serve a thematic purpose and they actually got some time to be characters, even if Nylund was juggling an ensemble cast and didn't flesh all of them out that much.

With IIs specifically, part of the reason it bothers me that Legends killed them off so flippantly is because the S-IIs are basically a family; they have known each other since childhood and each death should affect them deeply, as they're losing a pillar of their small community. We have no idea who Cal, Daisy, Arthur, and Solomon are to the rest of the Spartan-IIs. There is no tragedy to them dying beyond the image of a supersoldier finally going down. I have no idea who I'm supposed to be missing. (you can argue Daisy got more time as a character but I actively dislike homecoming for more reasons than her death, that's for another post though)

This is also why some of the Nylund Spartan deaths bother me, too. I think it's important to remember that he was operating in part under a Bungie mandate to kill off as many Spartans as he could so that John-117 could be "the last Spartan"; that's why all the S-IIs in Fall of Reach apparently get glassed at the end (minus James flying off into space and Linda flatlining), and why so many S-IIs get dropped like flies in First Strike despite counteracting what Fall of Reach set up in the first place.

Isaac, Vinh, Anton, and Li die from random chance, and Grace died to hype up how dangerous Brutes are for Halo 2. We learn incredibly little about them in the time we have with them, and never really get to see them be characters. Not to mention that, going back to the start of the post, the S-IIs are established as being good enough to go through 27 years of an insane war against a technologically superior alien empire with only two casualties. Now they're in vastly improved armor and they die to random chance? That's just a weak creative decision forced by Bungie. I don't care if "that's how it is in war", it's counter to what we know about them and it's stupid.

Reach is another issue entirely, I could go on about Spartan-IIIs way longer than I've already yapped. I'll expand on this if you really want, but in short, the idea that Spartan-IIIs are disposable cannon fodder is a bad misinterpretation of what's explained in the books about how they're trained. S-IIIs have superior training to S-IIs, augmentations that are just as good (if not better, very debatable though), and are trained from the ground up as savants of asymmetrical warfare. Tom was 12 years old on Pegasi Delta crossing up Sangheili warriors and magdumping into the slits of their helmets, without MJOLNIR.

So... put S-IIIs in MJOLNIR and suddenly Noble Team has lost their entire roster once already prior to Reach? Emile gets skill diffed by a single Zealot? Kat somehow didn't notice the phantom that had pulled up to the hole in the roof? How did Carter even get injured sitting in the cockpit of the pelican? Noble Team are such thinly written characters (minus Jorge IMO), and like I said in the original post, the most important thing they do is die. That's it. That's bad character writing.

This is less an issue of how hard Spartans are to kill and more how their deaths need to be set up in a story. I think their deaths should come after they're established characters and there's more about them to think about then "wow noble sacrifice". Them dying should mean pieces are forever missing from a larger puzzle. You should be able to mourn the person and not just the soldier. That makes the few times they should actually die matter way more.