And here we are coming back to your perspective of doing exclusively low keys on a nonlinear scale. You haven’t even encountered a scenario where the tank might just get smashed.
Key scaling isn’t linear. The damage multiplier on a +10 is almost twice what you’re used to on those +7s. With Fort on top of that, mobs are doing almost three times base damage. Certain key pulls are almost twice as big, and they might come with emissaries that also haven’t even encountered yet.
Let’s illustrate this in terms of one of the only two dungeons you’ve ever attempted.
Take those adorable little raptor packs. You probably haven’t noticed because they barely tap the tank, but those random pounces are actually really dangerous to everyone else. Last week, they each hit twice as hard as you’re used to, and there’s twice as many per pull. And oh look at that void emissary with no nearby LOS because lol open bridge – that’s an unavoidable 50% max HP nuke, which might overlap with an unavoidable 20% max quake, and if you don’t focus him down to the exclusion of everything else on the field and give the raptors more uptime, he’ll get a second cast that hits twice as hard and insta-wipes. So your party gets shredded out from behind you 4x harder and several times longer than you’re used to seeing, on top of all the added nukes.
Or maybe that 5-pull in front of Priestess? Now it’s an 8-pull plus a Tides emissary, who makes the whole thing immune to CC, stuns, and even interrupts, and the Tides itself hits pretty hard. Have fun with that pull also doing about 4x as much damage as you’re used to, plus uninterruptable hexes, venom bolts, and wildfires. You might try having the healer spam root the Tides every 4th GCD so you can handle the other 8 mobs “normally”, which means the party gets 1/4 less healing while fighting that massive pull. And the healer might have to additionally interrupt or delay other casts as quaking happens, and oh dear why are people dead now?
This is actually what we adapt to fastest. Raiders are very used to spacing out nukes, anticipating incoming damage, prioritizing gradual enrages, and finding ways to give the tank breathing room. That’s the bread and butter of modern raids. Pretty much every affix was ripped wholesale from raid mechanics.
Our shortcoming is generally that we don’t know the intricacies of trash, what specific live control is needed on who, and what pulls can be safely overlapped.