both harishima and tobirama were too stupid to become hokage. Harishima lacked "tsunade" attitude. He basically did not know how to run a village. Tobirama was too scared of the uchiha. He never thought of the uchiha's as equals.
Harishima gave weapons to the other villages so that the other villages are more "balanced" in power. Well, harishima gave those villages a taste of power and they used that power to start the second great ninja war. Cloud village constantly trying to get possession of the tailed beast. Even the other villages destroyed uzumaki clan because they wanted their sealing techniques for the tailed beasts.
Tobirama fueled hatred into the uchiha. What madara told the uchiha at the end of the day turned out to be right. An uchiha would have never be able to become a hokage. It was a silent fight that the senju were winning without fighting. They managed to get the uchiha to get rid of madara. They managed to isolate them. Even sarotobi did not want an uchiha to become the hokage. Sarotobi said himself " uchiha itachi" had the potential to become the hokage at young age but he basically didn't do anything to stop uchiha itachi to kill his clansman. The reason is simple, an uchiha who had the potential to become hokage was about to become the criminal that everyone in the village will know. Uchiha Itachi had a great chance of becoming the hokage and this is what Saratobi feared the most.
I have seen many occasions that tsunade went against the elders and higher ups. She never did what they asked of her. Yet saratobi let the elders dominate him because he wanted to be dominated. Deep inside of him, he didn't want an uchiha to become the hokage. At the end of the day, the uchiha were trying to seperate from hidden leaf village because they would never be treated as equal. All they had to do was to have a talk and tell them that uchiha itachi would be the next hokage and that they would no longer be isolated and treated differently. This would have stopped the uchiha from trying to separate from the leaf.
It is to be expected of sarotobi his resentment towards the uchiha. He was the student of tobirama after all. Sarotobi was chosen to be hokage at good age before uchiha itachi was even born. Many years had gone away, saratobi did not do anything to get the uchiha back into the hidden leaf village and the uchiha were still isolated even with the introduction of the new hokage. First hokage was a senju, second hokage was a senju, third hokage was a senju.They were still isolated. Uchiha village had all the reason in the world to try to separate from the hidden leaf village.