Yeah, it looks more difficult on paper, but in practice it's not bad.
I used my own Mash, a friend's Merlin, and my own Euryale (only half-skilled) and that took me through the entire fight completely unscathed. I swapped Euryale out for Dantes when it came time to deal with Amakusa, but really any Berserker or Avenger would do as long as you off him before his buff-wiping NP can do too much damage.
In the end, everyone was practically full health. Mash will tank ST NPs with taunt+invul, Merlin will protect you from AoE NPs. Garden of Avalon paired with Mash's defense skill and Lord Camelot will keep you in good health.

The one CS I used was actually against that goddamn massive ghost from the main event story, it gave me more trouble on its own than this final challenge did.
It's worth a whopping 3 tickets and some nice mats, so at the cost of only 5 AP to run it, I'd honestly recommend trying it at least a few times even if you're unsure about it.
Edit: Even if something catastrophic happens, you can use command seal revives if you make it at least to Amakusa or Dantes, because reviving at that point means you basically have the fight in the bag already.