Garrosh Normal 10 doing vastly different amounts of damage to different players

I been raiding a long time, but could not quite explain something I saw tonight. Multiple abilities on the Garrosh fight were doing wildly different amounts of damage to players. It wasn’t a bug but the mitigation % numbers in WCL also don’t add up.

Iron Star hit the wall? Half the raid was fine, the undergeared resto sham … well he took not just more %, but 100k more damage. Resto druid? Same thing

The whirl? Half the raid was laughing it off, the other half was mashing their healthstone button hoping that shtuff would work a third time.

https://classic.warcraftlogs.com/reports/YwL7fCAbDknaV4Tv