When Ichigo fought Aizen, Aizen's power after merging with hogyouku is 1 dimension above the level of regular shinigami and so his reaitsu cannot be felt. When he got pissed his raised his power level another dimension. Ichigo's power is even higher than that since Aizen cannot feel his strength. Thus, Ichigo's strength should be atleast 3 dimensions above the rest.
Now Yamamoto's reaitsu at bankai was felt by the other shinigami's, which shows that Yamamoto's power still belongs to the first dimension. Juha Bach killed Yama only after stealing his bankai, so if Yamamoto still had his bankai, it would atleast give Juha some trouble.
Now we know that Ichigo basically merged with his Hollow/Zangetsu so he no longer has the hollow mask and all of that power is now part of his bankai. This means that Ichigo who now is in bankai mode and confronting Juha should be at the power he fought against Aizen.
Moreover, we know that the difference in level of strength of shikai compared to bankai is 5-10 times. But bankai's reaitsu is still in the same dimension as shikai, hence if a person's power level is 1 dimension above, his reaitsu should be atleast >bankai strength = 10 times stronger than shikai.
But if that is the case, then Ichigo's current power should be atleast 10*10*10 = 1000 times greater than yamamoto's shikai's maximum reaitsu. This makes him atleast 100 times greater than yamamoto in strength when yama is in bankai mode.
Thus, Ichigo should have no problem beating Juha. If he loses, then there has to be an explanation. It has to be that he got a nerf, I won't buy it if they said Juha is just stronger cuz that is too bullshit.