Try switching to blessed hammers. helps with the low haste problem. Holy Shield just needs more haste to get the AM up faster in pulls, especially with only have 2 charges by default.
What i find interesting though is that AMR recommended really low haste for Holy Shield (5% haste) and then recommended nearly double haste for Blessed Hammers (9.5%). Seems backwards to me, as holy shield definitely needs it more to be viable in dungeons.
But yeah, it seems a lot of people are talking past each other. One side wants to talk about survivability and how the numbers add up to better survivability and the other side wants to talk about it not feeling right. I think the AMR script for mythic+ is missing a bit when it comes to tanking dungeons. With low haste right now on the holy shield talent, it takes a lot of gcd’s to get things going and to get agro of a pack…we lost our snap agro generation that we had in BFA. No more running in and popping our shield to aoe and get agro and have AM up. Now we have to generate it and with Holy Shield (recommended talent) it takes a bit. Having low haste just makes that worst. Yes soloing its fine, and the survivability is great, but man is it a pain in real world scenarios.
For others in here, try blessed hammer talent till you get more haste. Lets you cast before hand and generate some holy power to be ready.