Everyone is frozen. If this isn't a timestop then at the very least it can stop people's movements.
This proves nothing actually. It could be a inner dialogue with Natsu or something only related with Natsu. Also if this is something like movements-stop magic it worked against fodders. Admirals are tiers and tiers above those fodder soldiers.
The same question still remains...why Zeref will use it if he never did it twice in any other situation, battles included? And that's not time stop since the dust or smoke or whatever isn't froze.
Everyone of those instances you listed were moments he didn't need to use it.
- Stop Gray to freeze him
- Get back Mavis
- Stop Makarov escape plan
- Get back the book of END
- Stop normal Natsu during their last fight
And zeref doesn't need to have love as he literally has a death spell (the one he used against hades.)
During that time Hades was turned into a normal, badly injured, old man without magical powers, less than a fodder. Obviously that attack was enough to kill him like every other attacks. And it was just a spell, not a Death Magic. Never stated to be a Death Magic...it's a low-range magic and also requires time before being shooted. Every Admiral can dodge it effortlessly.