Instead, they've proven to be the biggest upgrades.
"We take pride in that, being physical," said Jackson, a first-round draft pick in 2005. "Nobody really knew anyone here besides Bob (Sanders), and I think we've all done that - made a conscious effort to be more physical."
Opponents understand now.
Back then, opponents thought they could beat the new starters.
Yet the replacements, who are bigger, faster and better maulers, have produced better results. Hayden ranks third on the team with 117 tackles; Jackson is fourth with 112. They've combined for four interceptions, 17 pass breakups, three forced fumbles and helped the Colts (13-3) ascend to No. 2 in the league against the pass.
No quarterback has thrown for more than 260 yards against Indy this season, not even MVP Tom Brady, who had 255 yards in November.
"We are aggressive guys," Jackson said. "There's a confidence there because I know we're all going to fly around the football and hit guys."
The bigger impact shows up on film, where Hayden and Jackson are often seen stopping runners and rarely missing tackles.
Replacing cornerbacks isn't supposed to be this easy, which is why so many questioned the Colts' offseason strategy of allowing both starters to walk away as free agents.
Coach Tony Dungy never fretted.
"We knew what we had," he said. "It wasn't accidental that we drafted Marlin and Kelvin and Antoine (Bethea) and Bob, and when the time came to decide not to match those offers, that was one thing we discussed. We knew these guys could run and hit."
From the moment Dungy arrived in Indianapolis in 2002, that was the plan.
The former defensive back told team president Bill Polian he wanted to bring the physical, ball-hawking style he adopted in other NFL cities to Indy.
"It was something that came up during my first discussion with Bill in 2002, when he said, 'What does it take to make this defense work?"' Dungy said.
The answer: Getting physical.
They took hard-hitting Sanders in the second round of the 2004 draft, then chose Jackson in the first round and Hayden in the second round in 2005, envisioning three eventual starters.
A year later, they chose another hard-hitting safety, Bethea, in Round 6, and Dungy finally had the foundation for a revamped secondary.
Sanders, this season's NFL defensive player of the year, and Bethea delivered results immediately after breaking into the lineup, while Hayden and Jackson refined their skills for the next two years and became virtually forgotten.
Until re-emerging during last year's playoffs.
"I look for Marlin and Kelvin to really step up and do a good job for us, and I think they've responded because they know this is their time," defensive coordinator Ron Meeks said during training camp.
Have they ever.
Taking the cue from Sanders and Bethea, Jackson and Hayden have caused chaos for opposing receivers with their pressing style. Those that dare to catch passes in front of them or try to run around them usually get clobbered, and Dungy couldn't have diagrammed it any better.
"That's just the way we are," Jackson said. "I know what Bob brings and what Kelvin brings and what Antoine brings and we know we're all going to hit guys."
Copyright 2007 by The Associated Press