Even if certain mechanics are more an individual effort there were mechanics way before Seph Ex that required the whole party to pay attention - and if one person messed up, it could mean a wipe.
Garuda EX - Kill spiny to early - the whole raid is dead. One person (or even one Egi, always lovely) was enough to mess that up. (Also: stack in the bubble to avoid damage - not so different from stacking to share damage, right?)
Titan EX - people used to bait the puddles, specially the doppel-ones in the last phase. Proper stacking and simutaionsly dodging was required to dodge them.
Ifrit EX - Nails were killed in a specific order, to make sure that they all died while no one was to close to the healer that had this bomb-thing. Theter out two people together, who had to stay clsoe to each other. Ifrit charges required the whole group - except the one bomb-healer, careful! - to move together.
King Mog EX - aaaah, beautiful! No one kills a moggle early, please! Watch out - is there someone else attacking the moggle your chewing on? Is someone interrupting that BLM - or do you risk it to give it a slap and eventually mess it up for everyone? Also: Did you make sure that there was at least one dps close to the paladin, to avoid both healers getting confused? (That mechanic targets the three people closest to the paladin and puts this moggle-confuse on them - one will hopefully be the tank tanking the paladin, the two others shouldnt be both healers...)
Leviathan EX - Whos getting the shield-thingie? Is everyone attacking the adds? And who the hell is pushing Levi down when he really shouldnt take anymore damage?! (Granted, this one most likely requires not a lot of effort when it comes to coordination)
Ramuh EX - KING of coordination! Do tanks need orbs? Should the party clear them? Is it safe to break the theter - or do we have to let tanks them first because thats more important? Is someone getting the charmed people? Did both of them made it to A or not? (And why is that dragoon standing next to me? Aaaaaah, ramuh will kil... ah, yeah, dragoon dead, cool)
Shiva EX - Stack behind her to share sword, dont stack for staff and ice puddles. Everyone make sure they got their safespot for that. Stack behind her to bait avalanche, BUT! make sure you move out of that if you dont have the blue mark!
For HW-primals...
I cant really think about mechanics like that for Bismarck and Ravana - Bismarck because it probably has non and Ravana, because its been ages since I've done the fight properly... and I dont have it down as much as the ARR-primals. However:
Thordan EX - Get your towers! Stack infront of the healer! Stack with the marker - on the tank, please, but dont stack when you have the other marker! Granted, they said they overdid it with Thordan...
...I can go through the other HW-primals, if you like? But let me tell you this: All fights are pretty scripted. You can learn them by heart and if everyone knows whats happening, no team coordination is required, because everyone know what they have to do and where they have to be at any given time. Stacking in Sephirot? Easly an individual effort - you just have to know where you have to stand. Can one person mess that up easly for the whole group and wipe them? Sure - but that was already the case with the very first EX-primal, Garuda. Now, that everyone is either doing ARR-primals unsyched or way overgeared you dont see a lot of mechanics anymore. No surprise that it seems that there are non and that those primals never required coordination - when they did, infact. A year from now, the towers and stacking in Seph wont matter anymore either. Healers will be able to heal through the damage and he will be dead before the blue puddles even have a chance to mess with you.
Primals are simply not a solo-challenge. If you want a solo-challenge playing an MMO is probably a bad idea.
You dont recall those mechanics because you didnt do those fights when they were current content, as you have stated a few times in threads regarding this issue. Today you can recover from three dead people in Shiva EX - but did you know that she has an enragetimer? Actually, she has two - adds have to die fast enough and she gets stacks of her damage up buff (goes up to 16, at 12 you're pretty much fucked - and even if you consider Shiva attractive you dont want that...). To mayn people die - thats about it for the raid.
I've seen Zurvan parties recover from people dying to soar or messing up theters. Two people messing up theters is nasty, but you can still clear the fight.