Also what is going super-tryhard?
"Try-hard" means playing only champions strong in the current meta or using "cheesy" or "cheap" tactics. If you only play Lucian ADC, Thresh/Morg/Braum support, Gnar/Ryze top, or Kha'zix jungle, you might be a try-hard (or you might just coincidentally happen to main champions that are currently strong). If you set level 1 bush gank traps or always 5-man invade at level 1 or have the jungler camp a single lane to oblivion, you might be a try-hard. There's nothing wrong with trying to win, but I guess the perception is that there are 2 reasons to play the game (not counting having fun): winning MMR/LP and getting promoted to get rewards, and improving your skill to make the first one easier. If all you do is "try-hard," the idea is you won't learn as much because you're restricting yourself to a certain champion pool and play-style, and the moment the meta shifts, you'll be SoL. There's also the idea that if you're a "one-trick-pony," you may not deserve your ranking because you just got lucky that your strongest champion was also one of the strongest champions in the game.
Elo-hell is everywhere
Statistically, Elo-hell doesn't exist, because, assuming you're not a feeder/baddie, the other team is more likely to have feeders than your team. To me, Elo-hell is any place where you can't carry yourself out despite being better than everyone else. If you're not significantly better, or you play low-impact roles, you won't be able to clearly carry your way out. You might have a slightly higher win rate than the other players in the game, but when you lose a game you had no control over despite playing much better than your lane opponent and your teammates, a 60% win rate is small comfort. Also, games are often decided both ways by other lanes, so you end up losing (and winning) games you have no control over, and even though it statistically evens out, people have a way of interpreting it as, "I lost games I would have won had I taken the feeder's lane from him, but those freebies where the other team fed, I would have won those anyway because they were bad!"
So I guess you could say half of Elo-hell is mental (victim of your own confirmation bias), and half of it is being "near" (though this is really subjective and dependent on specific circumstances and could be as much as an entire tier) your peak. You're good enough that statistically you win more than a player at your MMR should, but not so good that you get there quickly, which makes sense since if you could reach your "peak" that quickly, it wouldn't be your peak in the first place. Of course, having to play tons of games to reach something you're sure you deserve is tedious, and I could certainly envision a hell where you're forced to play League continuously, surrounded by toxic players, yet never able to progress in rank. The amount of butt-hurt in this game is certainly greater than anything a pitchfork could inflict.
poor decisionmaking is nigh-universal
Decision-making doesn't exist in a vacuum. You're gambling on the other guy being stupid (relative to you). Bluffing can be a significant part of lane dynamics. The stupidity (or brilliance) of a decision depends on the result. That stupid Baron throw? That would have been a brilliant call had it worked. That Trist/Kat/Kha'zix who jumped into the enemy team for the kill? Would have been brilliant if he got the kill and reset all over their faces. Why didn't he anticipate the shield and heal? Initiative and the element of surprise are powerful weapons; maybe he thought that would be enough. The decision was stupid because the other team knew what he was going to do (jump in for the kill) but he didn't know what they were going to do (heal in time). That's not something you can know for sure until after the fact, because it requires getting in the other guy's head. The difference in a Diamond's bad decision vs. a Bronze's is that the Diamond has a much better grasp of both what the Bronze is capable of, and what he himself is capable of. Their actions cannot be taken in a vacuum, because that Diamond will stomp all over the Bronze doing things that would get him annihilated against a similarly skilled opponent.
It's like hitting a skill-shot. He knows you're going to try to hit him. You know he knows. He knows you know that he knows. Do you aim at him? Do you aim at the side? Do you simply walk up to him while he's wasting time trying to juke you? It's a mind-game. Hitting that skill-shot means out-mind-gaming your opponent, same as any other decision in the game. If you aim to the side anticipating a dodge, you'll look just as bad regardless of whether he was a Diamond and expected you to predict a dodge, or a Bronze who simply didn't react to it. You'll also look just as bad as a cross-eyed Bronze who can't hit a stationary target.
Going back to the "bad Baron call." You gambled; you lost. If you had it to do over, would you do it again? It looks bad in retrospect, but maybe things really were that desperate. It's not a throw if you weren't in control in the first place. There's no point in slowly, hopelessly bleeding to death if there's even the slightest chance that gamble could pay off. There are so many little things that need to be considered that calling a decision "poor" is really unfair, unless you're merely taking responsibility for your own failure. The things you learn from the "bad Baron call" are also extremely subtle. Some might be obvious like, "Don't Baron before 20 minutes unless you aced them," but even that has exceptions like, "unless you have Nunu with max consume." And going back to the mind-game concept, the flip-side of this is that people learn to not check Baron before 20 minutes because it's a waste of time and wards. Of course, this is precisely what makes the early Baron gamble viable. Really, the only bad gambles are those whose expectation value of return is less than 1. You can't even be sure what the expectation value of return is in a game like blackjack (you can increase your odds by counting cards), how would you know whether that Baron call really
was a poor decision, other than superficially from the result? And even if you were counting cards, even if you remembered precisely every card dealt and calculated the exact odds of winning each hand, you could still lose, and you'd look no different than a noob who played every hand as if from a fresh deck.
TL;DR A "poor decision" means you got outplayed. Someone has to lose and it's disingenuous for an observer to call it a "poor decision."