Do what Slashley said.

Sanahtlig states that 40k Attack (that big red number on the top left of the main page screen) and a full grid with around Skill LV 14 (opposed to all the way up to 20) Assault weapons would suffice to take down Advent Ragnarok.

The faster way to build that grid would be killing the Expert Disaster 3 times per day, plus aiding at Ultimate Raids against Disasters. When team is strong enough to tackle Ultimate without support, do Ultimate Disaster 3 times per day instead, and aid at Ragnarok, for weapons with assault, Eidolons to sell for Orbs and some material for Soul Weapons.

Dreamlitz posted some vids of him taking down Guild Orders with teams around that level (40k Attack, dunno about his grids), but his approach is more defensive. After watching him taking down Icarus and Reiki, I realized a team could have two or more characters with the same buffs, depending on the content. For example, I managed to tackle Guild Order vs Icarus with both Cursed Chanting Chains and Wind R-tier Caspiel's Def Up (the 2 are A-Frame Defense Up), for the mission of having 3 R himes. The idea was to always have Defense Uo, cycling the two skills whenever the duration of one was over.