During that time the company - and Powell's leadership - have been scrutinised, with analysts speculating whether his resignation announcement this year was the result of a push from the board, after market impatience about slow bottom line results.
But Powell says his term was only ever going to be five years. "I can understand as we've gone through this journey, people will say, well there doesn't seem to be immediate results yet - profit hasn't increased, share price has gone down, and that's a fair enough question," he says.
"So then it's my job to non-defensively explain what we're doing and explain honestly that we're going through this change for these reasons and yes, that involves risk but we believe this is the right direction."
I think we tend to try and create this image that there are these people, these CEOs or boards who know exactly what's going to happen and get it right, but business involves choices and risks and making informed decisions and some things work and some things don't.
Before Powell taking over as chief executive, The Warehouse had been through seven years of declining sales. Powell was brought in to turn that trend around, which he has achieved.
Asked if he has done everything he wanted to during his term, Powell laughs. "You never achieve everything - business involves risk and judgment calls.
"I think we tend to try and create this image that there are these people, these CEOs or boards who know exactly what's going to happen and get it right, but business involves choices and risks and making informed decisions and some things work and some things don't."
In his time at The Warehouse, he says the toughest time was the death of 39-year-old Stephen Small, the company's chief financial officer, who died of a heart attack in May last year.
As well as the personal tragedy, Powell describes Small as one of the smartest people he had ever worked with, and leaving a "huge hole" in the company.
Overall, however, Powell is happy with where the company is.
For me coming into this role, I had a very specific job to do, which was to reverse a trend and reshape the business both in terms of the red sheds and non-red.
"You have to be looking forward and making decisions that will take a business forward," he says. "So have we got more right than wrong? I think we have. Are we well positioned after the reshape? Yes, I think we are. Am I pleased where I can leave and Nick can take over? Yes. But is it a lovely perfect story? No, because retail continues to be competitive and there's still a lot of work to do and there always will be."
Powell says Grayston's experience in the retail sector, which includes senior leadership positions at Sears Holdings, will serve him well.
Grayston will join the company next month and Powell will leave early next year. He says his time will be split. One day a work he'll be the CEO in residence at Massey University, he'll continue work on the board of electronics retailer The Good Guys, and he'll finish his Masters in Apologetics - the theory of religion, to add to his existing degrees.
"For me coming into this role, I had a very specific job to do, which was to reverse a trend and reshape the business both in terms of the red sheds and non-red," Powell says. "A lot's been done but the journey never ends in a business like this, especially in retail. They say you need to be healthily paranoid in retail because things can change very fast, but I think we're at a good point now."
The company's strategic work and refurbishment programme appears to be paying off, with the latest full-year profit coming in above forecast at $57.1 million.
As Powell heads off, all eyes will be on the incoming Grayston to see what he can do with New Zealand's biggest retailer.
Profile
•Job: Chief executive, The Warehouse Group, 2011-16
•Age: 53
•Born: In Wales
•Education: Two bachelors & two masters degrees
•First career: In mining
•Moved to New Zealand: 2002