The Danzo we saw fighting Sasuke was holding back, and would had also suffered weakness from age despite gaining new powers. Itachi himself hadn't shown signs of mastery of any MS jutsu except Tsukiyomi. Orochimaru was also dying and not trying to kill Itachi.
That is a lie. Danzo was being prudent, using only as much power as he needed so he could run a gauntlet.
Amaterasu is a fireball, it isn't instantaneous. If it were, MS Sasuke needing EMS to fight Naruto is pointless since MS Sasuke could one-shot current Naruto... that is not the case.
A Danzo that was older and slower, and lacked concern. He used Izanagi for defense, just as Itachi uses Susanoo for defense.
Only if Danzo stared directly into Itachi's eyes, which he will know not to do since he's an Uchiha.
In a one-on-one fight, one would hope Itachi could prevail by himself.
When did Danzo show fear of Tsukiyomi?