Sainz scored him maiden Formula 1 win at the British Grand Prix in early July, a week before his team-mate notched up his third of the campaign in Austria.
However, neither have graced the top step of the podium since then, a race Sainz retired from, with the Spaniard just sixth in the drivers' championship with two races remaining.
Despite Ferrari's early-season pace, the 28-year-old initially struggled to gel with the car, and by the time he could extract its full potential, Red Bull had moved the game forward.
“Probably the start of the season, those first six or seven races, when the car was the most competitive,” Sainz said when asked what the main reason he'd fallen behind Leclerc has been.
“He was doing the pole position, winning the races, you know.
“And lately, obviously, I've got a lot more up to speed and I'm driving a lot better the car, but also it's true that the car is not maybe at the level that it was at the beginning of the year – or let's say Red Bull has stepped it up.
“And it's not easy to score a pole position or win as it might have been at the beginning of the year.
“But he's done a better job than me this year, clearly, both in driving and race execution,” he added of Leclerc.
“He's felt, straightaway, more at home with the car than me, and I've been on this fight through the whole year to try and get myself to a similar level to last year.”
Last year marked Sainz's first as a Ferrari driver, managing 164.5 points over the 22 races to outscore his team-mate's 159.
New regulations introduced for the current campaign have shaken up the pecking order, with the Prancing Horse mounting a championship challenge with Leclerc for a time.
It was a marked improvement on the team's 2021 aspirations, which made a podium a noteworthy accomplishment for a team that hadn't won a race since Singapore 2019.
As the year as worn on, tyre degradation has proved an Achilles heel for Ferrari.
Since the Belgian Grand Prix, Red Bull has won every race, with Max Verstappen becoming champion elect at the Japanese Grand Prix – an event Sainz aquaplaned out of on the opening lap.
While there are clear deficiencies with the F1-75 versus the RB18, Sainz admits he's still not completely at home in the car even now.
“I think I still have a few things with this car that still don't come naturally,” he admitted.
“I'm now at a decent level, where I'm confident that I can score some good results and be consistent with it, but I look forward also to next year's car and see if I can get straight away more on the pace.”
Pressed on what specifically he was still struggling to get on top of, Sainz wouldn't be drawn into specifics though did offer an insight.
“There's just cars that you drive them and you, without even looking at the lap time, you know you've done a good lap and there's not going to be your team-mate or someone else going quicker than you,” he began.
“And then there's other cars that you think you've done a good lap time but it's not going to be enough because you've done some mistakes here or there.
“Then there's cars that you need to think while driving, and these cars that you [don't] drive naturally, and this year, while driving, I need to think a lot, I need a lot of head-space to know that this kind of corner I need to do it that way these kinds of corner I need to do it the other way.
“I'm sure there's hundredths, thousandths of seconds [that] go away while you're thinking about the corner that is coming.
“It's okay, I can do it, I mean, I've been pretty quick lately, especially over one lap, but it's still not ideal for a racing driver.”