Turner, speaking to Football Presse, said promotion itself had already exceeded expectations.
“There was no expectation last season of achieving promotion,” Turner said.
“The achievement of that was absolutely unbelievable.”
He praised the side’s dramatic play-off triumph after looking second best for long periods.
“To get into the play-offs, to get into the final, then on the day be outplayed and go 1-0 down, it could easily have been two or three,” he said.
“To then get a goal back late on and win 2-1 was unbelievable.”
Turner believes the club were then forced to accelerate plans once promotion was secured.
“I’m sure prior to the play-offs there was no building for the Premier League season,” he said.
“They suddenly found themselves in the Premier League.”
That led to significant spending, but Turner says the key has been intelligent recruitment rather than headline names.
“They went out and spent £150m to £200m on players that I don’t think many people knew who they were,” he said.
“But the recruitment from Sunderland last summer and the previous summer has been nothing but outstanding.”
Turner contrasted that success with clubs who have struggled despite larger reputations.
“Recruitment is everything,” he said. “You can spend money, but you need the right players and the right characters.”
Sunderland’s performances have impressed him just as much as the results.
“The performances so far this season have been superb,” Turner said. “They’re inside the top 10 and deserve to be there.”
He believes the club now have the platform to establish themselves in the top flight.
“To be fair, the way they’ve performed, you would say they’ll finish inside the top 10 this year,” he said.
“They should now be trying to establish themselves as a regular Premier League team like your Brentfords of this world.”
For a club that spent years outside the top division, Turner sees it as a remarkable turnaround.
“To go from where they were to where they are now is a huge achievement,” he said.