If you're going to include voice line triggers on boss fights then GIVE THEM A VOICE!
Why on earth would you develop an encounter with Nael in Unending Coil having a voice trigger for an ability with no actual voice? The only way to tell what she is doing at a certain point is to look for a chat bubble and read the text. This is a consistent problem relating to the game itself as a whole, not quite on the level of ability triggers of course but its still a problem. Many things that would benefit from a voiceover just simply are not voiced. I even feel like people who just skip the cutscenes would pay more attention if more voices were added to them other than a few random MSQs having it.