Here is some insight on how Hiruzen being able to use all techniques isn't a plot hole.
Hiruzen clearly used an ability that is like what the Bykugan does: telescoping vision across vast distances
So it's entirely possible for him to access KKG abilities via special tools.
He doesn't need...
Pain's Chibaku Tensei couldn't even restrain a half Kurama.
But Hiruzen's staff was able to knock a full Kurama out of the village.
Pain's ST couldn't even budge a 6 tailed half Kurama.
Hiruzen's staff>>>>>>ST
Hiruzen's staff>>>>>>CT
Manga fact.
Since ST and CT can destroy villages...
He could have used ST to destroy villages at anytime, so why did he wait so long?
Hiruzen. He wanted to wait until Hiruzen was dead so that he could attack Konoha.
Afterall, Hiruzen would have obliterated him.
You see, Hiruzen was going to die anyways. He was too old.
If Orochimaru didn't attack him, he would have died that day from old age.
Talk about a cheap shot. Attacking a man while he's literally dying.
Hiruzen was there.
If Hiruzen went, he would have completely obliterated the Kinkaku force.
Even though he was a kid, he was still had more power than everyone. Definitely more powerful than old age Hiruzen. By 30 times at least.
Hiruzen's old age was the greatest handicap of all time
Yes, it was worse than Itachi's disease. It was more debilitating than Kimimaros dying moments.
Heck, if a young Hiruzen was given a handicap with no limbs and blind, he can still out perform old Hiruzen.
That was how bad the age...
Emphasis on the SLIGHTLY
Hiruzen would have completely obliterated Oro along with the Edos with ease. Manga fact
He was deathly frail and old, so of course he lost. But he still put up a good fight.
Kishi stated in Databook 1 that Prime Hiruzen is the strongest of all time.
Kishi had numerous chances to retcon this. He didn't. Even in Databook 4, he made no indication that someone was stronger than Prime Hiruzen.
There is no evidence to show that Prime Hiruzen isn't the strongest.
But...
No matter how absurd it may seem, manga facts are manga facts. Databook facts are manga facts.
Also Manga Fact
.
Databook 1, Page 119
"History's Strongest", "Genius", etc., there are many words that describe the Sandaime Hokage.
His reasons are much better than Madara's, Obito's, Nagato's, or Sasuke's.
Indra became evil because of the extremely severe trauma inflicted upon his psyche when his father gave the inheritance that was rightfully his to his younger brother.
Indra is the man. He should have been the one to...
I believe Prime Hiruzen had the ability to use sage mode.
The Monkey King Sage Mode
It is the strongest of the sage modes, based off of the Monkey King, Son Wukong.
It most likely makes him nigh invincible as he would be able to use Son Wukong's powers, that is magic and immortality...
Manga fact, Yata is invincible
Also manga fact, Hiruzen is the strongest
Databook 1, Page 119
However invincible Itachi is, Prime Hiruzen is even more invincible because he is stronger by manga fact.
Also, Hiruzen is stronger than Kaguya, who can bust a dimension. Therefore Hiruzen...