it wasnt. hiruzen was less than 20m away and oro lol'd and summoned hokages as a mere shield to block.
1) Itachi is faster than Hiruzen
2) Hiruzen was throwing shurikens and had to weave 5 seals. Itachi will be using an attack that requires no seals, in which he simply looks at Oro, and nails him. One so fast, it nailed Tobi before he could react. Oro won't even have finished weaving the 4 seals (plus hand movement) before he's on fire, especially as Itachi is much faster. He also needs time to put the tags in. No happening.
so even if itachi wants to use genjutsu (he has never used it from such a range), it wont be useful anyway because
Itachi can use long range genjutsu. Aside from the fact we've seen him use it from miles and miles away, we are also told by the HS in the manga "oh yeh, he can control people from long range". We've also seen him nail Oro with it pretty easy. Not seeing why Oro is suddenly immune to it.
ET is much faster than a susano slowly advancing from 50m away. also oro need not stay 50m away. itachi cant do anything from 50m away in less than a second which is all oro needs to fuse with the ground using attack prevention and run in snake mode to some secluded area. theres a forest just outside VOTE. if itachi loses him in there its over. and i doubt hed even have line of sight for ammy or genjutsu when oro has just turned around to run for the forest in snake mode.
Itachi is plenty fast. It's not unthinkable he can bridge the gap and seal them. After all, this is a manga in which Tsunade can travel hundreds of meters against the force of gravity, weighed down by hundreds of tonnes, aim a giant object, throw it and land all in the time it takes Manda to bite someone. Itachi is a very fast guy, and 50m's isn't very much for him.
The problem with Oro running is:
a) Itachi is faster than him, and
b) Itachi can mimic whatever seals/tech he uses, and follow him, so Oro will never get away. And since Itachi is faster, he will get a little closer each time Oro tries to run.
