By which point he's too late.
He tried to stop the coup too late. He discovered Orochimaru too late and even let him go the first time. And when he finally manned up to face Orochimaru, it certainly wasn't because he wanted to. It was basically forced on him by Orochimaru.
The uchiha solution only became a problem BECAUSE of Hiruzen's inability to deal with Danzo though.
That ain't on Tobirama.
We need way more context of those wars.
And also, Hiruzen had a way easier time just working off of the system Tobirama already designed from the ground up.
Had Hiruzen been a competent hokage, he would have tried to fix the supposed flaws of Tobirama's design, and incorporate his own ideas into them. He did none of that. Just inherited the system from tobirama(most of which is still used even today btw), and made it demonstrably worse by introducing a new position for Danzo as the Shadow Hokage.