The Spaniard, who moved from McLaren to the Scuderia over the winter, suggested Hamilton's achievements in the Mercedes were "impossible to judge" due to modern Formula 1's "machine-driven" nature.
But with seven championships to his name, six of them coming since his Mercedes move in 2013, is there any credence to the claims that his genius is overplayed due to the car?
Power talks...
It has been no secret that Mercedes has been the powerhouse of the turbo-hybrid era in F1.
Ever since this breed of the power unit was introduced in 2014, the Silver Arrows has looked unstoppable bar two seasons in 2018 and 2019 when Ferrari gave it a run for its money.
If you go back to the beginning of this portion of F1 history, the gaps splitting Mercedes and the rest of the field in qualifying and the races were astonishing, with Williams the main benefactor of circuits with multiple long straights allowing some competition for Hamilton's team, Austria being the prime example.
Of course, last season, Max Verstappen was able to push Mercedes at various races, but there were still points in the season when it was as if the frontrunners were in a different race compared to the rest of the field, such was the margin of supremacy.
It is worth noting such dominance is not only down to the power capabilities of the German manufacturer's engine. The low-rake philosophy was recently copied by Racing Point - now Aston Martin - during the 'Pink Mercedes' debacle.
Other than this, no single team has opted for a low-rake concept, instead, taking a more traditional, high-rake stance seen in the aggressive Red Bull set-ups.
So partner a dominant engine with a design philosophy unmatched by any others and it is hard to see how parity could ever be reached. Unfortunately for Hamilton, the Mercedes performance has often detracted from his personal achievements.
One of the main points here is George Russel's performance in last year's Sakhir GP, finishing just 0.026secs behind Valtteri Bottas in qualifying and only missing out on a win due to a botched pit stop and a late puncture.
Did that prove that any driver worth his salt can jump in the Mercedes and land it on the front row and push for a win?
Hamilton vs team-mates - total domination?
So given that his car has been the class of the field, there has only been one person for Hamilton to beat, in theory - his team-mate.
During his entire career, Hamilton has only finished second-best in his team twice - to Jenson Button in 2011 and to Nico Rosberg when the German won the title in 2016.
In these years, the margins between Hamilton and his team-mate were 43 points in 2011 and just five in 2016.
He tied with Fernando Alonso in his rookie season at McLaren in 2007 with 109 points, before outscoring Heikki Kovalainen by 73 under the old points-scoring system.
With Button as a team-mate, Hamilton actually lost the head-to-head points battle by 15, largely down to his poor 2011 campaign filled with incident, although the pair were regularly on a par with each other - 2012 seeing Hamilton's lead over his team-mate at just two points.
Despite his title win in his final season before opting to retire, Rosberg was outscored by 139 points over the four seasons.
In the same time frame, Valtteri Bottas has been outscored by an unfathomable 430 points, including last year's 124-point deficit in just 17 races.
Your biggest rival is your team-mate and at a team in Mercedes that has seldom employed team-orders, Hamilton has only been toppled once.
Over a career, he has lost out twice in 14 seasons. That is a remarkable record and perhaps proof that he is one of the best, regardless of car performance.
F1 alumni - how do forner drivers fare in other circles?
The crux of Sainz's point revolves around what the rest of the grid is able to do. Very few are afforded the opportunity to battle upfront on driving talent alone, although last season, the Turkish Grand Prix ended up being a walk in the park for the seven-time champion as his driving skills saw him waltz away from the rest of the pack.
But Sainz's beliefs can be reflected in what former F1 drivers have been able to achieve since departing the series.
Kevin Magnussen was one of the stars of the recent 24 Hours at Daytona sportscar race. It was his debut, yet he pulled off the best overtake of the race and pulled his team back into contention in his first stint in endurance racing, despite the calibre and experience of others in his category.
Marcus Ericsson, who rarely featured in the top 10 in F1, is a leading IndyCar driver after just two seasons. Driving for the famous Chip Ganassi team, he is yet to emerge victorious from a race, although regularly battles in the top five.
Pascal Wehrlein and Jean-Eric Vergne are performing superbly in Formula E - the Frenchman picking up two consecutive titles in the sport.
Kamui Kobayashi is an established name in the endurance racing world, winning both the Le Mans and Daytona 24 Hour races as well as the World Endurance Championship.
All of these drivers were off the pace of the leading runners in F1 yet have displayed excellence in other forms of motorsport.
These are just some of those who have left F1 in the hybrid era. There are plenty of other drivers who have shown they possess the skill required to perform at the highest level.
Of course, Hamilton's achievements come from him being the best driver in the best team. It is unfortunate that his records and performances are questioned due to the dominant nature of the Mercedes.
Hopefully, the Briton will be around for the new regulation set being introduced in 2022 and be able to - for his sake - disprove the theory that it is the car doing all the work.