That wasn't quite the point IMO, but no one will convince me I am wrong about this (as either a mistake or design error). And I know my reason for changing it is not for symmetry, but because it represents the concept that larger monsters naturally should deal more physical damage (the scaling factor). This is a consistency which makes for good monster design.In general, @Ruin Explorer 's point is quite right - it's a bad idea to look for excessive consistency in monster design.
Which hopefully they did, but given how thorough they are I doubt it. I am fairly certain it was a conscious design choice--more's the pity.But in the specific case, it's possible that someone made a mistake.