When Orochimaru was summoning Minato's coffin during his fight with Hiruzen, Hiruzen through some shuriken at the coffin and peformed a hand seal. This gave the impression that he used a jutsu to cancel the summon. This became known as Hiruzens mysterious neutralizer jutsu.
As time marched on we found out that the coffin didnt go through because Minato was sealed within the RDS and thus could not be summoned. And so the legend of Hiruzens Neutralizer jutsu has become a stigma representing how people have overrated Hiruzens abilities in the past. When ever anyone feels like Hiruzen is being overhyped they make reference to his neutralizer jutsu to remind people that a mistake like this was made before. But it falls on deaf ears because we all know that hiruzen is a bad ass!
Hiruzen threw the shuriken first, Orochimaru summoned the coffins as shields. Hiruzen saw the first two, quickly deduced that they must be the other Hokages and knew that there would be a 3rd which he intended the stop the summoning of. He did a handseal and the coffin's summoning failed, to which point Hiruzen said that he stopped it in time.
As time marched on, we learned that Orochimaru would had resurrected Minato first and THEN placed him in the coffin until he needed him. So whether or not Minato was in the coffin, Hiruzen stopped it from being summoned.
Old Hiruzen is stated to being more powerful than Ei, Onoki, Yagura, Gaara Sr., Danzo, and was still a challenge for 100% Orochimaru whom was established as a threat to EMS Sasuke and without arms could toy with KN4 and was still more powerful than Hebi Sasuke. In Hiruzen's prime he was stronger than Tobirama, Minato, and Orochimaru. He is a master of taijutsu, genjutsu, and ninjutsu, and it's stated you need to use the 8th gate to surpass him. Even now while old he's referred to as one of the strongest in relation to Hashirama, Tobirama, and Minato.
Give the guy the respect he deserves.