The Italy striker signed a four-and-a-half-year contract at St Mary's Stadium after arriving for a reported club-record fee of £17 million.
Once regarded as one of the most promising starlets of Italian football, Gabbiadini had flattered to deceive at Napoli despite a respectable maiden season at the San Paolo.
The 25-year-old failed to hold down a place in Maurizio Sarri's starting XI over two seasons, often playing second fiddle to Gonzalo Higuain, Arkadiusz Milik and Dries Mertens.
However, Gabbiadini insists onlookers have been unfairly critical of his stint at the Serie A title challengers, and urges people to look at his numbers.
"I want to dedicate one final thought to those who have often criticised me and willingly labelled me as a football player with little personality and charisma, unable to withstand the pressures of the large stage at a big club," he wrote on Facebook.
"Well, what to say, I do not want to answer in words, but I prefer to talk about the numbers.
"In football, numbers are everything and capture the facts, in a Napoli shirt I scored 25 goals in 3119 minutes, a goal every 124 minutes."
Gabbiadini also revealed took advice from former Southampton striker Graziano Pelle in switching to Southamton, saying his international colleague played a significant part in his decision to move to the south of England.
"The great determination that Southampton had to purchase me from day one, and all the things that Graziano Pelle, who was my former team-mate in the national team, told me about Southampton," he told reporters.
"I spoke a lot of times with him in the national team and he suggested to me that it was a place to absolutely come and he's happy for me now that I have made this decision."