Uchiha and senju were considered rivals during the times of the war. When one group hires senju the other hires uchiha
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What ive got the gist of quiet some time aswell is that, whilst the uchiha were stronger man for man, the strongest amonst both clans was a senju, hashirama senju. If we were to take both hashirama senju and madara out of both clan's, i believe that the uchiha arent as dependant on their leader as the senju and would beat them if both leaders were taken out of their respective clans
If we were to take things currently, then the uchiha are stronger than the senju. The strongest LIVING uchiha is obito, edo madara is zombie. In fact if we were to go by what is currently happening in the manga and compare the current clan members i think its fair to say, obito would mop the floor with tsunade and the same can be said about ems sasuke.