The England international was forced to play a bit-part role during his 30-month spell with Manchester City, with 34 of his 73 appearances for the club coming off the bench.
Johnson endured a slow start to life on Wearside following his summer move but has gradually earned himself a place in Martin O'Neill's side.
The 25-year-old, who has netted four Premier League goals this season, including the winner against his former club City last month, is enjoying being a regular fixture and feels his recent form is a reflection of that.
He told The Sun: "At Manchester City, once players come in and you start coming on as a sub, you do get classed as a bit of an impact player. Even when that's probably not even true.
"But, at the end of the day, it is nice to be playing week-in, week-out.
"I think I've started more games for Sunderland than I did in the whole of last season. That tells you the story. My game is definitely benefiting from that. I feel much better physically."
Ex-Middlesbrough man Johnson was among the goalscorers as Sunderland saw off West Ham 3-0 in the Premier League on Saturday but the winger insists his own scoring record is not important as long as the Black Cats are winning.
"I did get 12 at Middlesbrough but that was in the Championship," he added. "But an assist is just as good as a goal for me."