Quick Hit Versus Doublecast

I see Quick Hit as the recommended method of dealing with basically everything late game in Final Fantasy X.

Why isn't Doublecast ever recommended for dealing with anything late game?

EDIT:

Doublecast is Rank 3 and Quick Hit is Rank 2 (on the remastered versions of Final Fantasy X.)

This means that you can get in 3 spells to every 2 attacks. Presumably every attack does 99,999 damage late game, so it seems like Doublecast would be better.

The damage done to Penance by a Maximum Magic character under the effect of Focus x 5 is 39,000: http://www.gamefaqs.com/boards/643146-final-fantasy-x-x-2-hd-remaster/69088560#5

According to the answer to this question Magic +20% is applied directly to the damage dealt by an attack based in that stat, so: the damage dealt to Penance would be 46,800.

Since Doublecast will do Ultima twice you're looking at a total damage of 93,600.

With Maximum Strength and 170 Luck you can do 99,999 critical damage per hit against Penance on a Quick Hit.

Since the Rank of Doublecast is 3 and the Rank of Quick Hit is 2 This means you'll get 2 attacks to every 3 casts, so your actual attack damage would be: 199,998 and your actual cast damage would be: 140,400.

If we use Penance as the gold standard of Doublecast versus Quick Hit, Doublecast is about 70% as effective as Quick Hit.