We know that Dojutsu users can see the power level of their opponents just by looking at them. For example, Nagato, who had the Rinnegan, looked at Sage Jiraiya emerging from the smoke and said that his power was similar to Orochimaru. (One of Minato's Father's arguments) The same goes for the Byakugan and Sharingan.
In my argument, Sarada with Sharingan, who saw the power of Deepa and Lord Ku, said that Jugo is very strong when she saw his power. Lord Ku scales to Kurotsuchi. Even though Kurotsuch did not focus well in the fight, he used jutsu and in this series, when you use jutsu, your power increases. A punch with a doton should be stronger than a normal punch and if you can concentrate enough to do jutsu, why should your jutsu be weak? Kurotsuchi's lack of attention is more the reason why he lost.