FLORHAM PARK, N.J. — For three games, Adam Gase’s job as New York Jets coach was to design game plans without three of his top six skill players. No quarterback Sam Darnold. No tight end Chris Herndon. No wide receiver Quincy Enunwa. The result was a hard-to-watch offense that avoided the end zone as if it were a hazmat area.

Gase was heavily criticized for the failings, much of it unfair because he was handcuffed by the illness and injuries, but now that chapter of the season is over.

Darnold is back, Herndon is back and it’s on Gase — the so-called offensive mastermind — to put a respectable product on the field. His QB1 will play for the first time since Week 1, so the “Luke Falk alibi” doesn’t cut it anymore.

It’s unrealistic to expect the Jets (0-4) to go from a 10-points-a-game team to the Kansas City Chiefs in one week — Darnold is bound to be rusty Sunday against the Dallas Cowboys (4:25 p.m. ET, CBS) — but his presence should make the operation run smoother. There should be some progress. There should be baby steps, followed by more steps in the second week of Darnold 2.0.

With Darnold, the beleaguered offensive line should have fewer breakdowns because of his smarts at the line of scrimmage. They should be able to move the pocket because of his ability to throw on the run, something the O-line couldn’t do with the immobile Falk. The Jets should be able to attack downfield, which will make wide receiver Robby Anderson happy.

In other words, Gase can use his entire playbook, not just the “Remedial Quarterbacking” sections. That should make a difference as they attempt to beat one of the deepest offensive funks in team history — only two touchdowns in four games.

“It’s probably more than just Sam getting out there — we’ve got a lot of other things to clean up — but Sam is able to hide things sometimes for us,” Gase said. “If we make a mistake, he covers it up.”

Quite simply, the offense couldn’t function with Falk at quarterback. In 10 of 16 quarters, the Jets have been led by a former practice squad player, which explains why they rank last in Total QBR in almost every situation — blitz, no blitz, in the pocket, third down, not pressured and play-action.

Darnold won’t be an instant elixir because, let’s not forget, he’s a developing quarterback with only 14 career starts. You can’t expect him to be at his best after a month-long bout with mononucleosis, which included three weeks of total inactivity. By Sunday, he will have had six post-mono practices, same as last season when he returned from his foot injury.

He endured some shaky moments in his first game back last season, Week 14 at the Buffalo Bills, but he settled down, found a rhythm and wound up directing an impressive win. The game included his signature play of his rookie season, that crazy scramble/touchdown pass to Anderson. It’s fair to expect a similar trajectory on Sunday — early rust, followed by a late rally.

The Cowboys (3-2) are ranked seventh in total defense, but it’s a soft seven because they got fat on bad offenses such as the Miami Dolphins, Washington Redskins and New York Giants. They’ve had trouble with tight ends, which could bode well for Herndon, who returns from a four-game suspension. The Cowboys have allowed 323 yards to opposing tight ends, which ranks 28th.

In a way, the Jets’ season re-starts on Sunday. It’s too late to make the playoffs, but it still can be a relative success if Gase fixes the offense and raises Darnold’s play by a notch or two. It’s all about Gase and Darnold. It’s time for the quarterback whisperer to validate his reputation.