I don't see why Tobirama shouldn't be capable of giving his brother a run for his money. If he fights Hashirama with power and large scales attacks then he'll definitely lose, and badly at that. If he's smart and utilises FTG well then he may be able to force Hashirama into a battle that suits tobiramas style.
The same way Obito cannot be defeated with big attacks and over the top jutsu, meaning you need to use feints, clones (be tricky and tactical), or win with speed or if you're fortunate enough to possess such an ability then space time ninjutsu. If Hashirama's giant large scale forests are useless against an opponent of tobiramas speed and s/t then there's no use in spamming it and eating the energy.
Thing is Tobirama will still lose even if wood release isn't used, simply because Hashirama is a fighting genius, whether it's taijutsu, kenjutsu, genjutsu and ninjutsu, Hashirama surpasses his brother in all these departments.
I'll say their gap in power is huge, but not in skill