"only sharingan can beat sharingan" theory is now D.E.A.D!
For a Jutsu that could supposedly only be broken by another sharingan, Hachibi destroyed it pretty easily. Deidara also proved that it's possible to overcome the sharingan, so Killerbee isn't even the first.
So, so long to Sharingan only beats Sharingan.
"chidori sword as unblockable"
O`RLY? We all know how this has ended up....