Tobirama was named as the fastest shinobi in an era where Hashirama (outran a bijuudama, physically matched Madara) and Madara (nigh blitzed SM Naruto, blocked V2 Raikage) were alive. Nothing Kakuzu has is catching him. His Katons get countered by Water Dragon, and in the unlikely scenario that Tobi is put in a hard to dodge position, he simply teleports to another part of the battlefield, seeing that he can easily dance around Kakuzu and his masks whilst still marking it.
Worst case scenario Tobirama outlasts him due to sheer stamina. But he doesn't have to.
As soon as he realises Domu is Doton, and that Kakuzu also uses Raiton attacks, he could set up a scenario where he's hit with his own Gian (mark Kakuzu, mark himself, have a clone touch Kakuzu when a mask tries to use Gian, then they swap, GG Domu).
Barring that, he could deal with the masks with Suidanha and explosive tag spam. Good luck to Kakuzu trying to hit Tobirama if all he has is Domu and a couple threads.
