The spiney has so little health that you can accidentally kill it, I don't even know why you're bringing it up.
You have a full 30 seconds after 2nd stack to pull spiny off OT, and if you "didn't notice" this fast enough, your tank is not paying attention and its HIS fault and its not a twitch mechanism at all. Wicked Wheel is predictable, always coming after friction after the teleport and the tank is responsible for popping CDs to mitigate the damage. You have nearly a minute to anticipate all of these things coming.
These are terrible examples of being "twitchy". This is just a case of reaction based gameplay and to be more blunt, simply paying attention.
Ifrit eruptions I'll give you, but arena wide plumes are not stacked like titan plumes and if you eat just 1, you will not die. Plus on ifrit, you don't need every DPS alive to beat him, and you have plenty of time to res people if they die on arena wide plumes or eruptions. Considering how he doesn't do eruptions or arena-plumes while nails are up, your whole point is moot.
And actually, you don't need to tank switch on Ifrit at all. A Warrior with high enough HP can eat every single breath, since it stops at 5 stacks and he'll have a little over 5.5k hp to eat attacks with. Again, you have like 2 whole minutes to switch after 2-3 stacks. This is simply paying attention, not "twitchy" at all. A good example of tank-switching is ultima, NOT ifrit. Even then you have like 2-3 minutes to switch tanks since stacks build pretty slowly on ultima.
You're clearly not understanding what I mean about "twitchy" mechanics and think I'm talking about simple "reaction based" mechanics, which are two completely different things.