By Matt Dolloff, CBS Boston

BOSTON (CBS) — Having a franchise quarterback is the biggest step toward building a Super Bowl champion. But it’s still only one step: the rest of the team matters too.

The Indianapolis Colts ostensibly tanked the 2011 season to secure the No. 1 pick in the 2012 NFL Draft, which they used to select consensus top pick Andrew Luck. Luck entered the NFL and instantly brought the Colts back to contender status, leading them to the playoffs in his first three seasons.

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But as luck battles through a treacherous fourth season in the league, the Colts remain riddled with question marks in key areas and still have an alarming lack of talent around their quarterback and defense. They should be legitimate Super Bowl contenders by now, but still feel so much further away than other top teams. How could Colts GM Ryan Grigson fail his franchise QB so badly?

The Colts enter Sunday’s showdown with the Patriots at Lucas Oil Stadium on a three-game winning streak, playing better after an ugly 0-2 start. But two of those wins came with Matt Hasselbeck at QB because Luck has been out with a shoulder injury – which happened in part because of poor protection by the Colts’ porous offensive line.

Through 5 games, Colts linemen have allowed 32 QB hits, 71 if you add up each individual player – which is good for second-most in the NFL. Change was necessary when Luck took 11 hits in the Colts’ 20-7 Week 2 loss against the New York Jets’ ferocious defensive front.

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The Colts re-tooled their offensive line after the Jets debacle, replacing two players and moving another – but the shocking lack of talent remains. The only offensive lineman the Colts signed in the offseason was the now-benched 33-year-old Todd Herremans, and they didn’t draft an O-lineman in the 2015 draft until the 7th round.

The Colts have moved the ball better since the major shakeup, and they handled Houston Texans All-World defensive end J.J. Watt well last Thursday. But the QB hits haven’t gone down much: they’ve allowed 15 in the last three games, after 17 in the first two.

Not only did Grigson fail to address arguably the Colts’ biggest weakness, he added expensive free agents and draft picks to an already-strong wide receiver corps. The Colts signed 33-year-old Andre Johnson, who was supposed to be the team’s big-bodied receiver to complement the speedier T.Y. Hilton. But before Week 5, Johnson had barely made a dent in the offense and been supplanted on the depth chart by Donte Moncrief, who they already had on the roster. They also signed veteran running back Frank Gore, who has been his usual solid self – but was not a necessary addition for a team with far bigger needs.

Andrew Luck has been under siege behind a fragile Colts offensive line. (Photo by Tom Szczerbowski/Getty Images)

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Two Colts signings that have actually helped the team are defensive lineman Kendall Langford and linebacker Nate Irving, who have helped improve the Colts’ previously abysmal run defense that the Patriots famously shredded in recent games. But they had a good opportunity to improve their run D when defensive tackle Malcolm Brown fell to them in the first round of the draft – but instead, stunningly, they took receiver Phillip Dorsett.

Even without drafting Brown, the Colts appear better equipped to contain the Patriots’ power running game with LeGarrette Blount – but they also haven’t faced an opponent nearly as talented or well-coached on offense as New England, nor have they faced a QB in the same universe as Tom Brady.

Despite a slightly improved run defense, the Colts have been torched through the air in 2015. Through Week 5, Indy ranks 28th in the league with 287 passing yards allowed per game. They’ve generated little pressure on opposing QBs, totaling just 6 sacks – tied for 29th in the league. If the uninspiring lot of QBs they’ve already faced were able to throw without pressure, what is Brady going to do to them with a clean pocket?

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The Colts have been decent at keeping teams out of the end zone, allowing just 12 combined rushing and receiving touchdowns – but again, the quarterbacks they have faced are Tyrod Taylor, Ryan Fitzpatrick, rookie Marcus Mariota, Blake Bortles, and Brian Hoyer. And now they get Brady.

And of course, Luck himself has been part of the problem. He still turns the ball over way too much, throwing 7 interceptions in 3 games (!) and fumbling twice. But a weak offensive line will always exacerbate that problem, and his injured or ineffective weapons aren’t doing him any favors either. And much of the blame for that should fall squarely on Grigson’s shoulders.

The Colts should have learned with Peyton Manning that one player can’t carry an entire team to a championship. Luck alone makes the Colts a playoff contender, but to contend for Super Bowls they need more balance. Defense and pass protection were glaring needs in the past two offseasons, and Grigson made minimal effort to improve them – and in five games against average-at-best opponents, his negligence in those areas is manifesting itself on the field.

The Colts defense face their first real test on Sunday, and it has already been ugly for them against the pass. Add in all that other nonsense that I’ve purposely avoided in this article, and you have an extra-motivated Brady looking to embarrass the team that tried to embarrass him before the Super Bowl.

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The Colts haven’t gotten much better since last year’s AFC Championship game. On Sunday, the result will be more of the same. And Grigson’s failure to surround his franchise QB with enough viable talent will become that much more obvious.