Just adding my 2 cents regarding "you should never use vercure".

Vercure as well as verrais are emergency spells.
You ideally do not want to use them, but if the situation occurs you should. Basically, whenever you know (or have a very strong feeling about it) that you will die because healers won't be able to top u in time. In other words, vercure should be used to save your life (or someone else) but never to help healers.

It is your duty to recognize when the situation is dire and your healer can't keep people alive (whether it's their fault or not)
For instance, I recently did Shinryu and in p3 the healer forgot to move during freeze thunder combo, when the head came down he was freshly rez zed and obviously oom. The red mage tossed a few vercure to help on the dragon head.
Did it lower its dps? Absolutely.
Was it a Desirable situation? Obviously not
Would have we wiped without his intervention? Well, we'll never know but it would have been a very close call.

So just be smart about it