... I don't know whether to laugh or cry.
You determine difficulty on the basic of the most rudimentary tank mechanic that defines every single fight outside dungeon bosses? I'll be blunt. If this is difficult for you, you aren't ready to heal EX primals. Your personal struggles does not make a fight hard, but simply means you lack the experience. Nidhogg and Sophia were much harder fights when I was new to raiding. That doesn't make them difficult but shows my inexperience. Regardless, Tank busters are entirely scripted and among the easiest mechanics to deal with because they have little if any variance. Susano will always use Stormspliter at the beginning, and will use it again at the same point unless you skip the buster entirely. Good tanks will mitigate through this with little problem.
The rest of your post boils down to you lacking experience and conflating that to mean the fights themselves are difficult. You being unable to see the markers only adds credence to the above argument; you need more experience.