Sweden National Junior Team coach Tomas Monten is hopeful Westerlund can take that next step.
"[Westerlund] was in a tough spot and didn't get to play in Frolunda that long since he was playing a lot of junior hockey (in Sweden's SuperElit)," Monten said. "After the [2018 WJC] he was loaned to a second-division pro team (Bjorkloven of Allsvenskan) and his game took off.
"I think he'll be a top-six defenseman in Frolunda this season."
Gaining that experience will only help develop and prepare him for the rigors of the NHL. He joined other prospects during Arizona's development camp June 25-29.
"I felt really good at development camp," Westerlund said. "It was my second year. Last year was more about learning about the organization, and this year I felt a lot more comfortable in what I was doing; had more confidence."
Westerlund was one of the last cuts from Sweden's WJC roster last year. Monten said his staff chose Linus Hogberg (Philadelphia Flyers) over Westerlund as the seventh defenseman for the 2018 WJC because he impressed with more minutes in a shutdown role for Vaxjo (SHL).
"It was my goal last year to make this team but now it's more like a revenge situation for me," Westerlund said. "I want to get on the team and be a big leader."
Monten understands there will be an adjustment on defense without Dahlin, but he's confident in his group.
"You're not going to find a Dahlin, but hopefully you can find seven good defensemen," he said. "I was really lucky to get to coach [Dahlin] twice at the world juniors. He's an unbelievable kid and great player, and I think he'll do fine in Buffalo.
"I think we have good options on defense this year. We have a couple of younger defensemen that could step up."
He's hopeful Westerlund will be one of them.