The delay of Hallowed Ground is unacceptable

[zakalw3]

So everyone should be required to know a fight by heart before HG proves to be useful. Yep. Not broken at all.

You can predict when you'll need in any standard dungeon. This comes with practise and experience.

For specific, difficult boss battles such as Titan, then you can either study the rotations to learn the patterns or go via trial and error. Both ways will teach you when to use HG in advance.

So yes, it's perfectly usable. I use it constantly, and the only time I fail with it is when I'm not focused and don't realise I'm in trouble till it's too late.