Until the 4th ninja war, a Mangekyou Sharingan user had been showcased as a formidable enemy, with Genjutsu being one of their many powerful techniques. Itachi was adept with Tsukuyomi. Sasuke suppressed the Nine Tails' power with his Sharingan when Naruto faced him in Orochimaru's hideout.
It would be fair to consider that both Tobi and Madara are equally adept, if not better, with the Genjutsu abilities of the Mangekyou Sharingan. However, in the 4th Ninja War, they do not use Genjutsu much.
It could be argued that a Sharingan user may be able to cancel out Sharingan's Genjutsu, but Genjutsu could still be effective against a non-Sharingan user, such as Naruto or Bee.
Tobi could easily put them under Genjutsu and take over their tailed beasts, but he has not done it. He did not use it on Guy either when they fought.
Is there a reason why the Sharigan users did not use Genjutsu in the 4th Ninja War?