Tobirama was also able to transform(condense) the moisture in the air into water for his attacks,when there literally was no water source.And his attacks were very strong despite where or at which altitude he was at(for this reason he was known as the strongest water style user).He didnt need seals for his water attacks,an testament of his exceptional chakra control.He even could transform an opponents water attack into his own.
He could do high level of genjutsu and possesed advance taijutsu skill.He knew space time ninjutsu and had sensory abilities.When a ninja is controled by edo tensi and his emotions are ended by the edo tensi user,the ninja is weaker and does not fights to its full potential,thats the reason tobirama seems weak.There is nothing more to say!