With seven starters returning to the same scheme under the same coordinator, the Giants’ defense was supposed to take a step forward in 2023 — maybe even two steps, if the splashy additions at middle linebacker and cornerback paid immediate dividends.

Instead, the defense mostly has taken steps backward after allowing first downs … and steps sideways to miss tackles.

Everything but steps forward … except for an occasional encroachment penalty.

The Giants missed 16 tackles, allowed an astounding 201 yards after the catch and didn’t force a turnover on Thursday night in a 30-12 loss to the 49ers.

That happened though the Giants made quarterback Brock Purdy rush his decision-making by blitzing at the highest single-game rate percentage (84.6) of any NFL team over at least the last seven seasons, according to NextGenStats.

“Their playmakers were just making plays, and when we attacked, we would get to them late,” defensive tackle Dexter Lawrence said afterward. “There were a lot of screens that we didn’t get to. We all have to run to the ball and go get it.”

But the defensive issues are bigger than one game.

The Giants are allowing a league-high 32.7 points per game and are ranked No. 24 of 32 in total defense (361.7 yards allowed per game).

More than 53 percent of opponents’ drives have resulted in a score — a number that is better than only three other teams.

It might have been worse if the Cardinals hadn’t mistakenly retreated into a second-half shell and punted three straight times to fuel the Giants’ 21-point comeback in their 31-28 Week 2 win.

Whereas early season struggles were easy to forecast for an offense breaking in new weapons, defensive coordinator Wink Martindale set a high bar during the first week of training camp.

“It’s the second year in the system,” Martindale said at the time. “We know the players better, and they know us better. You can visualize what guys can do — we did that last year and it worked out well for us — but we also know there’s a lot of improving that we need to do because if you’re not changing in this league, you won’t be in this league very long.”

So, then maybe it’s a defense-wide sophomore slump.

“We’re trying to build this brick by brick,” outside linebacker Kayvon Thibodeaux said. “I feel like there were some spurts of the team that we could be. We just have to be more consistent.”

The Giants have been built like the other fancy houses in the neighborhood — heavily invested up front — but closer inspection reveals a crack in the foundation.

They are allotting the NFL’s third-most salary-cap dollars ($49.3 million) and outlaying the fourth-most cash ($58.4 million) to the defensive line, according to spotrac.com.

The quartet of Lawrence (2019 first-round pick with a fresh $96 million extension), Leonard Williams (carrying the highest non-quarterback salary-cap charge in the league at $32.3 million this season), Thibodeaux (2022 first-round pick) and Azeez Ojulari (2021 second-round pick) was the presumed strength of a defense.

It hasn’t played out that way during a 1-2 start, though a young secondary allowing 7.1 net yards per pass attempt (ranked No. 29) isn’t blameless, either.

“We need more from everybody: Coaching, playing, everybody,” head coach Brian Daboll said Friday after a cross-country flight home. “The game is a line of scrimmage game at the start of it, but we need more from everybody.”

In their most recent matchups against the Giants, the Eagles (five sacks, four tackles for loss and eight quarterback hits during the 2022 playoffs), Cowboys (seven sacks, 10 tackles for loss and 12 quarterback hits in Week 1) and 49ers (two sacks, four tackles for loss and six quarterback hits in Week 3) have dominated one side of the line of scrimmage.

The Giants weren’t able to match that level of disruption.

They totaled three sacks, 13 tackles for loss and nine quarterback hits in those three games.

It’s no surprise then that opponents this season are converting 48.7 percent of third downs (ranked No. 26) and have advanced into the red zone 12 times to start this season.

Fifty days after Martindale envisioned familiarity breeding exotic looks, the Giants are headed back to the basics of tackling.

“That’s an area that’s got to get better,” Daboll said. “We’ll continue to find ways to help these guys be better at their craft in terms of bringing people down and wrapping up. Something we’ve got to work on.”

Baby steps for the Giants defense.