I think it's specifically designed to be survived easily by Relic Phoenix. If you look at their kits and shared uniques they're essentially perfect for surviving Sidious' AoE + Debuffs. It'll heal them all. Kanan's Zeta then clears everything and puts down foresight. Then daze/stagger like crazy. Only thing you're really missing is Tenacity Down.
Each of these Challenge Tier events is cleared geared to be easily beaten by 1 of the 2 factions available. The second faction can beat it, however; they need to be much higher geared than normal:
Rebel Roundup:
BH > Troopers (Can be do CT1 with G12 BHs)
Military Might:
Rebels > Clones
Ground War:
Jedi > Ewoks
But who wants to relic Phoenix?
I can't clear Tier 1 and I have 2x G13 NS and the rest are G12+0 to G12+2. Great but not top-tier arena grade mods.