as I was on holiday, Maz re-worked the mechanics to scale up to handle a group.
Re-reading your post before submitting this comment answered my questions but im gonna post it anyway incase it sparks anything else to touch on.
How do you feel the boss is doing scale wise for the players its designed for?
Seems to have a ton hp (400 hp, in comparison to godwars bosses at 255 hp for instance but they have way more def/hit harder and are group content) and a longer fight for players in the 70-80 combat stat range to solo.
I guess that leads to a 2nd question, was the fight/stats changed from when it was instance and definite solo only to accommodate noninstance/potential group fighting? Is it meant to be soloed by lv 100s anymore?
As you mentioned, god wars bosses have significantly more defense than Sarachnis does, her 400hp doesn't feel too severe from what i've seen.
I personally feel like a lower defence higher hp boss is more fun for players to fight because nothing is more frustrating than hitting nothing but 0s. Also she's a spider, spiders aren't known for having a high defense