The 23-year-old made significant progress last term, signing his first professional contract and making 12 appearances, including seven starts.
His standout display against Leinster offered a glimpse of his potential, but Duncan has returned refreshed from a holiday in Jamaica with ambitions to take another major step forward.
The departure of Jack Dempsey has also created an opportunity in Glasgow's back-row. The Scotland international was a hugely influential figure at number eight, but rather than being daunted by the prospect of helping fill that void, Duncan is embracing it.
Speaking to Scotland Rugby News, Duncan said: "It's 100% big shoes to fill, but I feel like it's achievable. You've just got to make sure you carry on the momentum.
"Obviously, I learned a lot from watching Demmo play. I feel like it's just honing in on my own skills and learning from what he brought to the team. Then just adding that into this season and my own skills package. Just putting my best foot forward within that role and sticking to the basics.
"As a back-row, my strengths would be work rate - that's my biggest strength. Around the breakdown, I just need to get my opportunities. Last season, I was a bit shy within the breakdown. You don't really want to put a foot wrong.
"This year, it's just going out there and putting in the best. Even if you make a mistake, just be happy with that. I want to improve with my ball carrying - that was Demmo's super strength. In tight spaces, for example, it's just footwork. Most importantly, I need to be a good team player."
Glasgow have not directly replaced Dempsey this summer. New arrival Ruwald van der Merwe can operate across the back-row, while Jamie Ritchie is primarily expected to feature at flanker and Matt Fagerson remains a leading option at number eight.
That could open the door for Duncan to increase his involvement after firmly establishing himself in the senior squad last season.
"I'd say it was a good season," he adds.
"It felt much longer and it flies by way quicker than you think. I felt my pre-season was a good run into the season, which then backed it up. It just helped out. All the older boys, they helped me out a lot. Matt Fagerson, Rory Darge helped out a lot.
"They helped pull me through, I feel. You just learn from them. It was an enjoyable season for me. You play with lots of big-time players, world-class players. Last season was just a stepping stone to leapfrog me into this season."
Duncan returned to Glasgow refreshed after his summer break, but admits he was more than ready to get back into the structured environment created by Smith and his coaching staff.
For the back-rower, the discipline and routine of professional rugby are something he thrives on.
"I'm buzzing to be back," he admits. "Being six weeks off is too much for me, I think. I wouldn't tell Franco that but six weeks off was a lot, so I'm buzzing to just get back in. It's good for me to be a bit more disciplined and having a regime helps out a lot. So it's nice to be back in this environment.
"When all the international boys come back as well, everyone trains. Once we're back in Scotstoun, I feel like it'll help out a lot to just merge the boys in. I can't wait for the season to get underway."
Duncan's focus now turns towards making the most of those opportunities, with the 23-year-old targeting a minimum of 15 appearances as he looks to establish himself more firmly in Smith's plans.
Predominantly a number eight, he can also operate at openside - although Franco Smith's willingness to experiment means Duncan has even experienced life further out during training.
Asked his preferred role, Duncan laughs: "Maybe at centre or as a winger. No, never. I prefer seven or eight. Last season as well, I got a little run in training as a back, as a winger.
"It's never going to be full-time, but if something happened, I feel like one of the more athletic boys would go on the wing. It could be me."
For Duncan, the challenge now is turning the promise of last season into consistency. His performance against Leinster demonstrated what he can offer at this level, and with opportunities available in Glasgow's reshaped back-row, he will be looking to make the most of them.