I used our last Ra-den log to see what EF was doing for me with the shield. This fight probably has the highest usage of shields from the HoT and even the HoT ticks themselves. Other fights would probably be less of a nerf than for this one.
I assumed 33% mastery.
As you can see it is a 6.92% nerf to total healing to remove the stacking of the shield. If you fully replace EF you will have to get 16.8% more healing from your tier 45 talent to break even with live…
Here is 50% Mastery: