It's all about the Resistance as Valli pointed out. Multi attack Avatars, such as Shiva, requires /nin. Other wise you can be one shotted by the multi attack tp moves. With those fights, we tend to use a Geo for Magic evasion bubble on the DDs, for more of a resistance build. These fights are very similar to the old Ouryu fights back in the day, where the pld needed a high resistance build.
Long as you can survive the 2 hours and high magic attacks, typically you'll be fine. It'll just be a matter of killing it before it wears out your whm.
Edit: We don't use pld on these fights btw.
Standard set up we use has been;
Whm/sch(or rdm sub) ~ done it /run as well for added resistance
Brd/whm
Geo(or extra DD) Depending on which avatar
DD/run or /nin ^
Thf after the recent update with Rudra just melts these nms pretty quickly as well and if you have a good mnk with mdt/pdt set, makes them a great SA/TA victim.
Save flash for when it two hours, use lunges and other tp moves when it uses either a heavy magic move or tp move to proc and basically stun it. Make sure the whm is far enough away to not get hit by magic attacks