What do we mean when we say "Carulli was a good composer but not as good as Sor".
Let's examine a little study of Carulli's and see if we can find an objective way of comparing his work with Sor's.
The Carulli study is Prelude 7 from Op. 114. I have excerpted the first eight measures for my example.
If we consider this piece to have a four voice texture and we examine the voice-leading, we notice that there are parallel octaves between the bass and alto (C-D) in measure four into measure five.
I asked myself what would Sor do? By simply changing the "D" (alto) in measure five to a "B" Carulli would have avoided the parallel octaves and actually improved the harmony in my opinion.
The new harmony that results in measure five is a Bm7b5 (or B half-diminished seventh if you prefer) in first inversion. This would now be labeled as a ii chord in the key of A minor.
Sor often uses this harmony, especially at cadences, as a substitute for the iv chord. Interestingly this creates a ii-V-i cadence rather than a iv-V-i which is preferred and often cited in jazz harmony.
Open the PDF below and compare the two versions and tell me what you think.
At least objective examples like this are one way of comparing the skill and craftsmanship of two composers. Most of us would agree that Sor was the "better" composer.