The championship window is rapidly closing on this iteration of the Phoenix Suns

What ails the 12th-place Phoenix Suns as a prospective playoff team has been diagnosed on the injury report daily. What ails the Western Conference's reigning No. 1 seed as a contender is more complicated.

The Suns fell from the final play-in tournament berth behind the once-forgotten Oklahoma City Thunder on another weekend when All-Star guards Devin Booker and Chris Paul were shelved. Last season's starting stretch forward, Jae Crowder, has not played since requesting a trade in September. This season's starting stretch forward, Cameron Johnson, required knee surgery eight games into this campaign. Of the top seven players who formed Phoenix's playoff rotation the past two seasons, only Mikal Bridges and Deandre Ayton have played two-thirds of their games this season, and even Ayton has missed a handful of games due to injury.

It isn't difficult to decipher why the Suns are 21-24 in mid-January. Their presumptive starting five has played just 67 minutes together in six games. They have also outscored their opponents by 43 points in those minutes, a glimmer of hope for Suns fans. Johnson is expected back "very soon" from meniscus surgery, Paul is day-to-day with a sore hip, and Booker's strained groin will be reevaluated next week.

There is still time. The Suns are one loss out of the sixth seed and a third straight guaranteed playoff spot.

Then what? It is a fool's errand to cling to small sample sizes as a predictor of playoff success, especially when the writing on the wall is unraveling on the court. For as good as their best five-man lineup has been in 67 minutes, the Suns have done nothing to quell concerns about the way they unraveled in a blowout loss at home to Luka Doncic and the Dallas Mavericks in Game 7 of the Western Conference semifinals.

Paul, 37, entered this season with 45,000 combined regular season and playoff minutes on his treads. Tony Parker was the last point guard to reach that milestone, and he couldn't make it through a full season once he eclipsed it. Parker came off the bench for 56 games with the Charlotte Hornets before retiring in 2019.

The Suns lean heavily on Paul. He still orchestrates the offense and takes care of the ball, even if his assist and turnover rates are the second lowest and third highest of his career, respectively. More concerning are his 13.1 points per game and 44% shooting on 2-pointers this season, both career lows by a healthy margin.

Worse, the Suns are losing by 3.6 points per 100 possessions whenever Paul is on the court, the first negative net rating of his 18-year career. The slippage is real. A sore right heel cost him 14 games earlier this season, and a sore hip has been keeping him out of the lineup for five more games and counting.

Meanwhile, Ayton, the No. 1 overall pick in 2018, two spots ahead of Doncic, is no longer on the rise. He spent two seasons committing himself to defense and accepting a tertiary role in the offense, only to be benched in an elimination game and left floundering in restricted free agency. Ayton eventually negotiated a four-year, $133 million contract with the Indiana Pacers, which the Suns immediately matched, and the ramifications for both parties have been underwhelming. He is drifting farther from the basket on offense and not protecting it as well on the other end, where 38 centers are statistically better at defending the rim.

Suns coach Monty Williams and Ayton did not speak during an offseason that began with the 7-footer's benching. The two were openly arguing about his defensive effort during a timeout in a loss to the lowly Washington Wizards last month, and Williams has since implored Ayton through the media to play harder.

Not enough has been made of the Crowder saga, either. Aging role players under contract do not demand out of a positive atmosphere. He made vague references to being underappreciated and "blindsided" by the coaching staff, and his teammates went on record with Bleacher Report's Chris Haynes to defend him.

Suns executive James Jones has further hindered the depth beyond the Crowder fiasco. He drafted Jalen Smith with a top-10 pick in 2020 and traded him with a second-rounder 15 months later for Torrey Craig. Jones also traded Jevon Carter and their 2021 first-round pick for Landry Shamet. Neither of them played a significant role in last year's playoffs, and Phoenix remains without reliable backups to Paul and Ayton.

For all the excitement about the Suns' depth of high-end talent emerging from the 2021 Finals, they can no longer survive minutes without Booker. They have been outscored by 22.5 points per 100 possessions with Paul, Bridges and Ayton on the court and Booker off of it. Two years ago, those same lineups were beating opponents by double digits per 100 possessions. Bridges is the only other player on the roster who has actively improved, performing at an All-Defensive level and making strides as a playmaker on offense.

Booker was competing at an MVP level when he rolled his ankle in a blowout loss to the Mavericks on Dec. 5. He played through the pain, only to tweak a hamstring and injure his groin over the next 10 days. He attempted to return on Christmas but aggravated the groin injury four minutes into his outing. The Suns are 3-15 without Booker in the lineup since mid-December, plummeting from third to 12th in the West.

It is reasonable to expect a surge once Booker returns, but to what end? Soft tissue injuries linger, and even if he comes back by the All-Star break, Booker will be left to carry a point guard in decline, a disengaged center who is feuding with the coach and another starter who is returning from in-season knee surgery. The Suns are six losses back from a top-four playoff seed, and we saw how a Game 7 at home ended last season. To expect them to navigate three road series en route to another Finals appearance is a tall order.

The malaise in Phoenix extends well beyond the season-long suspension of team owner Robert Sarver.

The Suns are in need of a shakeup. The lingering Crowder situation is a reflection of how little Phoenix can expect in return for a 32-year-old impending free agent whose commitment is in question. Their reported interest in Toronto Raptors guard Fred VanVleet is an indication that they are contemplating a near future without Paul — and rightfully so. His $30 million salary is non-guaranteed in 2024, when the Suns owe $107 million to Booker, Bridges and Ayton — before they deal with Johnson's forthcoming restricted free agency.

Is incoming team owner Mat Ishbia really going to want to pay $60 million annually to Paul and Ayton over the next two years, when they are providing half that value to the team? If not, who is going to offer equal value for either? The Suns can make the argument that the 24-year-old Ayton could resume his once-rising stardom with a change of scenery and attaching draft equity to his salary makes that conversation easier. Ayton became trade-eligible this week, though he owns veto power over any potential deal this season.

It was inconceivable that Brooklyn Nets superstar Kevin Durant would be in a more stable environment than the Suns several months after he requested a trade to them, but here we are. Phoenix reportedly offered "Bridges and a handful of first-round draft picks" for Durant over the summer, but that gained no traction. Now, the Suns are desperate, making them less attractive in trades, both as negotiators and a destination.

This is the end of the road for a once-promising team in Phoenix. Just as the Suns' Finals appearance begot their 64-win regular season, an embarrassing second-round loss has devolved into mediocrity, and it will take more than an aging point guard to turn their sinking ship around. The only question is whether Jones is creative and aggressive enough to reconstruct a contender around Booker before he sours, too.

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Ben Rohrbach is a senior NBA writer for Yahoo Sports. Have a tip? Email him at rohrbach_ben@yahoo.com or follow him on Twitter! Follow @brohrbach