Are RJ Barrett, Obi Toppin and Immanuel Quickley plateauing?

The pie-in-the-sky preseason optimism wasn’t about Jalen Brunson magically becoming a superstar. Or about Julius Randle performing like Giannis Antetokounmpo.

No, the hope that the Knicks would surpass outside expectations — their over-under win total set by the bookmakers, for instance, was 38.5 — was pinned to the development of their young players, the belief that internal improvement would raise this team’s ceiling. But through a quarter of the season, those players haven’t taken the step forward that fans, and perhaps the team, hoped.

RJ Barrett has underperformed at both ends of the floor after signing a four-year, $107 million contract extension. Obi Toppin has improved his 3-point shot, but his defense remains a major flaw and he hasn’t come close to pushing Randle for a bigger chunk of minutes at the four. Immanuel Quickley has been inconsistent. Quentin Grimes battled a nagging left foot injury, and only now is beginning to make an impact. Even Brunson, who has been the Knicks’ most reliable player, has faltered in being asked to be a go-to guy down the stretch of games when he is at his best as a facilitator.

The Knicks have a bunch of JAGs — Just Another Guy, as Bill Parcells used to say about players who weren’t difference-makers. And it is the overriding factor in the Knicks’ mediocre 10-12 start, as well as why they have yet to beat a quality opponent at home. All these young players have talent, but also faults.

Barrett — after scoring 26 points and missing a potential game-tying 3-pointer in Wednesday night’s 109-103 home loss to the Bucks — is averaging an inefficient 18.8 points on 40.6 percent field-goal shooting, not to mention a dreadful 28.1 percent from 3-point range. With Grimes out, Barrett was asked to be the Knicks’ defensive stopper on the perimeter and struggled in that role. His individual defensive rating of 117.3 per 100 possessions is second-worst on the team, ahead only of Randle’s 118.0. The Knicks have been outscored by 3.3 points per 100 possessions when Barrett is on the floor.

Toppin has remained a limited contributor, averaging just 17.5 minutes and fewer points (8.2) than he did a season ago (9.0). His 3-point shot has improved — up to 37.1 percent even with a recent slide — but he still is a work in progress on the defensive end. Grizzlies forward Jaren Jackson Jr. went around him like he was a traffic cone in the Knicks’ loss to the Grizzlies on Sunday.

Then there is Quickley, whose name has come up in trade talks. His advanced stats are strong — he owns the team’s top defensive rating (104.3) and second-best net rating (3.8) among regulars — and he has improved as a rebounder. But his offense remains uneven, as illustrated by his scoring in double figures in three of four games between three consecutive six-point efforts and Wednesday’s four-point outing. He’s shooting under 40 percent from the field at 38.7, getting to the free-throw line at a career-worst rate and only making 30.2 percent of his attempts from beyond the arc.

While Barrett has clearly struggled, Quickley and Toppin have not. But they haven’t taken major steps forward, either. As can be said about the Knicks as a collective in their first 22 games, there have been some good moments and some bad ones. And that doesn’t make for a team that can take any sort of step forward based on what is already on the roster. They just may be nice players with major flaws in their game.

Big problem

For now, Jericho Sims is the odd man out in the Knicks’ center rotation. Over the past three games, the second-year pivot hasn’t received any rotational minutes. He only got into Tuesday’s win over the Pistons because the game was a blowout.

It’s a mistake.

The 6-foot-10 Sims has played very well when given an opportunity. He’s averaging 4.7 points, 4.9 rebounds and one block in 13.9 minutes per game. He was instrumental in the Knicks’ two best wins of the year, on the road against the Nuggets and Jazz, and performed well in Friday’s overtime home loss to the Trail Blazers. His Player Efficiency Rating (PER) is 20.3, which entering Wednesday night ranked 39th in the league and second on the Knicks behind Brunson’s 22.28 (PER is based on a formula that adds positive stats and subtracts negative ones through a statistical point value system).

To be fair, Thibodeau is in a tough spot with Sims. The Knicks paid Mitchell Robinson and Isaiah Hartenstein a lot of money to be on the floor. Robinson should be. He’s too important on the defensive end and his offensive rebounding (3.8 per game) is such a strength.

That leaves Hartenstein’s minutes. Though Hartenstein is a better passer and has a more versatile skill set, Sims’ defense and overall activity offer an improvement over Hartenstein, at least recently.

The overall advanced stats aren’t in Sims’ favor, mostly because of the small sample size his 13.9 minutes per game represents and his extensive role playing in mop-up duty. But over the past 10 games, the Knicks are minus-14.5 points per 100 possessions when Hartenstein is on the floor and just minus-2.2 with Sims. In that same span, the Knicks have a 112.3 defensive rating with Sims and 122.4 with Hartenstein, per NBA.com.

But for now, it seems as if Sims is going to have to wait for a real opportunity.

Absence makes the heart grow fonder

A quarter of the way into the season, it’s clear Brunson’s old team misses him dearly. The Mavericks will arrive for a Garden matinee Saturday mired in mediocrity. The Mavericks, who reached the Western Conference Final last season with Brunson, are 10-10 after snapping a four-game losing streak at home on Tuesday night with a narrow win over the Warriors.

Though Luka Doncic has been unaffected, posting superstar numbers of 33.5 points, 8.8 rebounds and 8.6 assists, the Mavericks have missed Brunson’s shotmaking and playmaking.

As a team, they are averaging 21.2 assists, down from 23.4 a season ago, and shooting 34.4 percent from deep after making 35 percent last season. Maxi Kleber, Tim Hardaway Jr. and Reggie Bullock are each shooting below 31 percent. Hardaway, the former Knick, has really been struggling, and is averaging just 10.8 points on 32.7 percent shooting from the field.

In an ironic twist, Dallas this week signed Kemba Walker, the player the Knicks traded on draft night to help clear enough salary-cap space to sign Brunson. Maybe Walker, who didn’t fit with the Knicks in his one season with his hometown team, will help replace some of Brunson’s production, but considering no other team saw him as worth pursuing, that may be asking too much.