Linguistic similarities of 2 John and 3 John

3 John is also linguistically similar to 2 John.  These two letters shared 99 different words, but 21 were unimportant words like “and” or “the”.  Thus, there were only 78 significant words.  23 of these words do not appear in 1 John or the Gospel of John.  3 John has 4 unique words.  Approximately 30% of the significant words in 3 John do not appear in 1 John or the Gospel of John, compared to 20% for 2 John.  These considerations indicate a close affinity between 2 and 3 John, although 2 John is more strongly connected with 1 John than it is with 3 John.  Does this prove a common authorship of 2 and 3 John?  Is linguistic analysis valuable?