There is no way to button mash against a skilled opponent.The 33-50% shit is straight from the producer talking about if you're buttonmashing blindly because you don't know what the response to an attack is you're going to be right 1 in 3 or 2.
Everything can be blocked, or combo broke. It's backed by reaction, not some blind system of this will work 30% of the time...
Only unblockable attacks are the ones you throw yourself into i.e. Punish on block, and even those can be combo broke.