Wiktionary
a. Contextual comparative. Modifies another adjective (to which the "so" is a direct anaphoric reference), indicating a lesser degree of the quality in question.
Usage examples of "less so".
His amazing mind, too, was keen as ever, much like the marvelous Analytical Engine of Charles Babbage, which he greatly admired, if a bit less so having learned that the infamous Professor Moriarty had a hand in the inventor's mathematical logic.
I also like the epilogue where we find that some of the characters lived happily ever after some less so.
This does not mean that there were one hundred and fifty-seven aboard more worthy or intelligent than I, but on the other hand there were ninety who were definitely less so.
It was not a house to which I could think of bringing a bride, much less so dainty a one as Edith Bartlett.
The craft was banged up, but a lot less so than the engineer would have believed.
But that description had never really seemed accurate to her before, and now that she'd actually seen a 'cat with her own eyes, it seemed even less so.
Perhaps not the less so from feeling a doubt of my positive happiness had my fair cousin honoured me with her hand.
But really this time it was harder than she had ever found it, and once or twice she thought it almost made her more cold and hungry instead of less so.