I wouldn't call it difficult, just a little tedious at some bits, and some of the wink-wink-nudge-nudge stuff assumes you've played Samurai/Remnant because it will not explain the backstory, like why character X hates character Y so much. The Gamepress FGO wiki always has a walkthrough for every event you can follow to do it in the most efficient way possible, if you want to use it.
It's a normal FGO event, which is to say... the Welfare gets a 100% attack boost against everything, and you can get CEs that add an additional 100% damage (or 200%, if maxed). Put that on Iori and you should be able to kill anything, even with a newer account, so long as you can enter the event at all. XD