That's exactly what I'm trying to to say and you said it yourself pretty well especially @bold. Senjus were stronger because they had more at base and that was basically their full potential. Uchihas had more potential but unlocking that potential is difficult. That's exactly why Uchiha is the superior clan because they have much more potential compared to the Senjus, and if they utilized that potential they would be stronger definitely. And since they couldn't unlock that potential that's why Senju > Uchiha. Uchiha's powers rely a lot on Sharingan, without it Senjus are slightly better. Plus, learning Sage Mode has a lot more chances than awakening MS.
Senju full potential is basically only their base form which is slightly better than Uchihas without Sharingan due to larger chakra reserves. Uchihas powers depend a lot on Sharingan and without it, Senjus will obviously be superior. So Senju full potential < Uchiha full potential, but since Senjus are already at full potential, that's why they were victorious during Hashirama and Madara's era, because Uchihas weren't at all full potential.
Plus, talking extensively, Senju full potential is Sage Mode. Chances of learning Sage Mode > chances of awakening MS, though both are low.