Having just committed to extending his contract by another two years until the end of 2026, it is clear that McLaren sees a very bright future for the young Australian.
But it is not just his raw speed that has stood out during his early spell at Woking, because there are aspects of his personality that have deeply impressed team management – and reminded them of some of F1's greats.
"When McLaren so strongly wanted to sign Oscar, we looked at the results in the junior categories, and in the early days of the collaborating we could see what he achieved, there were good reasons for that to happen," explained Stella.
"We could see these in the natural speed, which if you want is related to the talent. We even saw it the first day of the simulator.
"The way he was kind of assessing his own performance, saying: 'This is where I am, this is where I need to improve.' It was matching so well with what we could see from the data, that it was quite impressive."
Stella thinks that strong understanding of his own performance is a powerful tool to help him improve.
"These qualities have to do with being able to continuously improve," continued Stella. "I'm sure there were a lot of people that were talented, but it didn't lead anywhere because there was no attitude to continuous improvement.
"I think we have really good examples now on the grid, of drivers that can keep being extremely competitive at ages that we didn't think would be obvious, because of an attitude to continuously improve. So, in this sense, I think this one is a similarity with Fernando."
It is not just how he empowers himself that impresses McLaren, it is the way that Piastri interacts with staff that is also impressing Stella.
"We have the person behind the driver," he said. "For us, it was important to make sure that the person that we keep on board is a person that not only fits our culture, but will contribute to establishing the culture even more. And potentially adding to the culture, adding to the values, and the behaviours that make us become a team of mates.
"The values he brings into the collaboration with the team, in this sense, makes me think about Michael [Schumacher].
"There is somebody who worked with Michael here in the paddock, who is at another team, he said to me he was so capable of building families.
"While it was definitely tough on track, within the team, the spirit, the sense of unity, there was no shortage of a sense of family. So, I think I'm referring to natural talent, attitude, culture and values. These three things became apparent to us relatively soon."
Piastri has also shown himself to be quite calm and collected when speaking to the media, and it is a behaviour that McLaren has seen him match in the garage too.
Stella added: "When you are in a pressurised environment, like F1, it becomes very important to be a calm, considerate person.
"He doesn't have nervous reactions; he doesn't have unnecessary irritation. He doesn't add tension in his comments. His comments are a genuine report of what happens with a car or a genuine report or what happens in a situation that wasn't ideal.
"You can trust what he's saying, and he's not adding speculatively anything because he needs to promote himself. He is trustworthy and calm.
"This calmness is a quality I generally try to strengthen as much as possible throughout the team."