As has been repeatedly pointed out by the Itachi-lovers, Oro has seemingly admitted to fearing Itachi's power.

But as to the main, or certainly implied, point of this thread: I too think that Oro's power is sometimes under-estimated. He is, in my opinion, the most powerful character revealed atm. Ofc, over time, we will see more weaknesses, and other characters will develop in order to exploit them - but I cannot in all honesty see any obvious vulnerabilities at this point in the series.