Hiruzen's literal nickname known throughout the world is "The Professor". His whole thing is being knowledgeable and knowing Konoha's every jutsu including clan secret ones. Orochimaru reanimates Hiruzen during the fight with Ten-tails to help Sasuke and later help the leaf. So in this situation, we have a person who has an immortal body, unlimited chakra and knows EVERY JUTSU OF THE MOST POWERFUL VILLIAGE. He could have used FTG to teleport between battlefields along with Tobirama and Minato, he could have sealed Ten-tail using any of the Uzumaki sealing jutsu, he could bind the Ten-tails with shadow possession, he could battle it one on one using the expansion jutsu, he could have burned it alive using HIS CLAN'S fire style, he could have used the 8th gate without any problems because his body was indestructible. Hiruzen had an idiotic amount of options but he used the bare minimum.
P.S.
How in the hell does he know every clan's unique jutsu. He can't know the Aburame clan's jutsu because he could not have bugs placed inside him he can't use Kekkei Genkais obviously, he didn't have a ninja hound so he could not use the Inuzuka clan's jutsu on top of that, he hasn't ever been seen using a White Light Blade so he wouldn't be able to use Hatake's jutsu which would come in handy considering Sakumo was rumored to possess more power than all of the Sannin combined, he doesn't have the 100 healing mark which means he doesn't know that jutsu either and the list goes on. Also, he refers to the Death reaper seal as "Forth's jutsu". How in the hell are you raised by a guy who is married to an Uzumaki, are the Hokage under whose rule your shinobi start wearing flak jackets with Uzumaki crests on the back and shoulders, are close with another guy who is married to an Uzumaki, and on top of that have relations with the hidden whirlpool village for a long time considering they were whipped out during the third great ninja war and still call the jutsu gifted to Konoha by the Uzumaki's as "Forth's jutsu"?
End of rant