The veteran midfielder was the only player axed from the Hawks' side which defeated Geelong in their qualifying final, making way for damaging half-back Matt Suckling.
Sewell, a two-time premiership star who played his 200th game against the Cats, paid the price partly because of the Power's explosive outside speed.
"That's part of it, but we just feel like we're better balanced," Hawks coach Alastair Clarkson said on Friday.
Versus: Lewis v Gray
"We've got a lot of inside-mids, particularly with the emergence of (Will) Langford who's played some really good footy for us in the second half of the year.
"We just feel like we've got a better balance with Matt Suckling coming into the team."
Clarkson said it was a tough call to omit Sewell, who has forged a reputation as a big-game performer in September.
"He's disappointed, I'm disappointed. He's been an enormous part of this footy club," he said.
"He's also fully aware that it's all about the the team and how we can best progress.
Watch: 2001 semi-final - Power v Hawks
"He'll hope that we win a preliminary final and put himself in the selection mix for next week's game."
Sewell is set to line-up alongside star forward Cyril Rioli in Sunday's VFL Grand Final for Box Hill at Etihad Stadium.
It will be the first game in 12 weeks for Rioli, who will only play if Hawthorn beats the Power, after his drawn out recovery from a hamstring tendon injury.
"He's ready to play. In our wisdom, we think the best approach for it is (for) him to get some confidence in his body at VFL level and get a run," Clarkson said.
"Does that guarantee him a game next week if we happen to progress? We'll just have to wait and see.
"We've been working on this over the last two to three weeks. We feel like and he feels like it’s the best preparation for him in terms of being able to make himself available to play more footy next week.
"He's really comfortable with it, we're really comfortable with it."
Saturday will be Hawthorn's fourth-consecutive preliminary final appearance, with the previous three decided by less than a goal.
Another epic could be in store against the Power, who will be playing in their first prelim since 2007.
Port triumphed by 14 points against Hawthorn in round 10 and Ken Hinkley's men have hit some of their best form in sudden-death finals wins over Richmond and Fremantle.
"They're an impressive side. They started the season particularly well and I think their rough patch through the middle of the year probably disguised the fact they were two games clear of everyone at about round 12 or 13," Clarkson said.
"They've returned some of that form the last five or six weeks, so we need to play at our best.
"That's what's required to win preliminary finals."
