I was searching for a way to quickly destroy the grunt goblin, and whaddya know? The fastest way to take down a Grunt Goblin- Halo 5: Guardians - YouTube
It seems that with a lot of TJM (Twin Jewels of Maethrillian) shots you can destroy that energy shield and insta-kill the Grunt inside. Hopefully this should help with the grunt goblins on Warzone maps (A.R.C and Apex) seeing that they are left alone for a majority of the match