Hi, regarding your usage of defensives, I like that you use Shield Wall early and prio getting Shield Block up on the opening pull of the dungeon rather than waiting until you've lost half your health.
You aren't using Demoralizing Shout (24 casts) or Shield Charge (8 casts) enough, which is both a damage loss and survivability loss. Demoralizing Shout is 20% dmg bonus while it's up, so send it on cd. Shield Charge gives Shield Block for free, so only hold it if you can hit more enemies with it a couple seconds later or you are about to have Demoralizing Shout back. This will also help on your SB uptime, which again contributes to your overall damage.
You use Spell reflect actively, which is good to see. I noticed on Corewarden Nysarra during Umbral Lash you use Shield Wall, but not also Spell Reflect. Since it's magic damage and the biggest damage intake for you in that fight you can freely use it - potentially not even having to use Shield Wall, saving the charge.
Your use of Shockwave can be a little haphazard. At least I see you casting it at full health, with SW up and nothing casted by enemies. Try to use it more as an interrupt or brief window of relief if you are taking heavy damage.
On talents you can consider picking up Battle-Scarred Veteran over Shield Specialization as a safety net. Melee hits are steady damage and not what will cause you to drop. I also see you are not running the 3% leech talent in the general tree - why not?
For gathering Charge / Heroic Leap to the bigger packs and use Thunder Clap/Blast as your primary way to gain snap threat. Anything you don't want to Charge to you use Heroic/Wrecking Throw. Be mindful which add packs have casters and interrupt them as you pull, Wrecking Throw is particularly useful for pesky casters at range. The goal should be to get them all into one stack as quickly as possible, without dying, so you can pop your cooldowns and blast. Don't have it like the last add pack you did before Lothraxion.