Another response that only proves you never set a foot into a mythic raid. But okay, I play along because it is quite easy to prove you are wrong.
First, the part about the 3 line script. While I agree that today almost noone goes into a bossfight blind, those who cleared Mythic HFC first surely didn't have a guide. So it is actually possible to say a certain raid tier was harder or easier depending on how long it took for a first kill or even a 200th kill. Then, if you actually play in Mythic environment, you will learn that those boss guides aren't a sure way to win the fight. They depend a lot on a given setup. If you have to play with another setup, you need to adopt. Thus, you will see a lot of different guides after a while, and even more different tactics used by raiding guilds. This is nothing new and was the same back in Ulduar.
As for gearchecks: There certainly are gearchecks. Like, you know, in BWL/OL, when you needed a certain cloak for a certain fight. Or like, you know, in AQ where you needed a certain resistance for certain fights. Or like, you know, even back in MC, where a certain amount of fire resistance were required. Today those checks are far more lenient and are easily achieved by just clearing the bosses before those checks a few times and distribute the loot in a smart way. Where is the problem in that?
As for bossmods, DBM/BW is nothing new. There where bossmods for Ulduar HMs as well. You would know that if you actually tanked hard modes back in Ulduar. There were even a certain mod in ICC that drew danger zones directly onto the 3d world. Got banned pretty fast. While Bossmods evolved quite a bit, and maybe offer to much assistance in some cases, it is clear that some encounter mechanics are designed with boss mods or even addons in general in mind.
As for threat, it was a non issue in WotLK as well. You would know that if you actually tanked hard modes back in Ulduar. Today, threat is only important for tankswaps and add spawn. Take a look at Xhul. You might be surprised how important proper timing is in this fight. For damage dealers, they have to adapt all the time. Save resources for burst phase? Can I use this cooldown now or do I need it to close a blackhole because our other soakers is affected by a debuff? Can I burst on the boss to force a transition before the next wave of adds spawn, or should I stop doing dps for a moment so we don't have a transition while adds spawn? Basically, you have to do decisions all the time. What you describe is Molten Core level of boredom where you have to watch your threatmeter while spamming frostbolt.
As for that /castsequence macro nonsense: Stop being an idiot. Like really. Please stop. It's like you never even played the game. If it where that easy everyone would run around in Mythic gear and ride that stupid Archimonde mount we sell for 1,2 million each week.
