When Reach is being invaded, it'll take at least one Spartan to escort her. No way would she go alone. And what would he do? What do you think? He's a Spartan-III, there's a lot he can do. Sure if a small army decided to swarm them, they may both die, but Jun can take on any Covenant Lance threatening Halsey. He was assigned a different mission altogether, one separate from the rest Noble's. There's no time to mention him again, by the end of the next mission the rest of Noble Team are dead. Jun is mentioned in other media. Reading your post right now has led me to realise you're looking at this from a "typical gamer's" point of view (not a bad thing). Assuming you have no problem with the reality of what happened and you're just voicing your opinion, I can understand your disappointment. I personally can't relate to it at all though, I feel like if things went differently, people would still criticise the same way. What happens, happens. You can't complain about real events not going the best way, people on Reach aren't gonna be like "There's a chance we could be in a simulation right now, so lets satisfy whoever's watching with a cool death.". As a general gamer, I wouldn't be surprised if many people didn't like what happens, everyone's got their opinion. But the reality is that they died how they did, and there's nothing wrong with it. Criticising Bungie is like saying "God didn't make their deaths/exits cool enough or ran out of ideas.", it just doesn't work that way.
I'll continue responding for other points not relating to personal opinion. B312 and Kat were only around 10 metres away from the rest of Noble. For a sniper that's a very small distance. By the time he spotted the first 3 and brought his aim up, Kat would've certainly been in his sight. I like what you said there about the Scarab, but what's even funnier is imagining Carter flying around a hundred times, strafing the Scarab's legs until he get it to drop, then shooting at the core at the back whilst B312 and Emile are just chilling. It wouldn't even work, keep in mind he's fatally wounded and in a Pelican, not a Banshee. Almost cracked a smile at Jorge's contract running out. How would Emile know the platform was swarmed? The dropship was behind him, and he was focussed on the zealot right in front of him. Him and the others in Noble are technically sailors, but that sounds a little wrong so you'd refer to them as Spartans. And yeah, he was a good Spartan, unfortunately not good enough to survive the encounter. Keep in mind zealots are very difficult to handle. The Elite probably wasn't dying until he finished it off, and if he was, he wouldn't just lay there. He'd get back up and make it a priority to kill Emile, read about the Sangheili and you'll get it. Unless they're dead, they won't drop and stay down. The other didn't really didn't just wait, he was making his way towards Emile and you can see that he's not there until he impales him. Yeah I agree Emile should have got the job done with more speed, but he may not have known there were others near him. I agree he should have at least glanced over, any professional warrior should have as much situational awareness as possible, but I think his flaw here is his natural personality/behaviour. Emile is real aggressive and sadistic, he was over the moon when looking straight at that zealot and blasting it to death with his shotgun. Potentially in a very mild and temporary state of euphoria. Zealots can stealth easily, like Spec Ops Elites, so it's not surprising to have one catch him off guard. I can imagine many other Spartans failing in his situation too. There wasn't long at all between the time he killed the zealot, and the moment he was impaled.
Almost all media produced by anyone is done for money, no point even mentioning it, but I'm confident 343 and Bungie care a lot about the lore. Microsoft's a different story. I strongly disagree with your last three sentenced. Halo is by far one of the most realistic sci-fi titles out there. You really need to read the books because the games are real limited on showing that. Most things listed in your first out of three last sentences are already being developed or have already been developed, but to a different extent. It's hard to comment on the realism without reading many books, the more you read the more you'll learn. Halo has the most realistic situation for humanity by its timeline, and there's no unrealistic combat I am yet to encounter. I urge you to read books before making further comment on the reality of anything, even though the games don't do a bad job either.