It's the facility boosts and every driver gets them, not just your teammate. Williams, Aston, Alpha, Alfa and Haas all get +5 to their stats while Red Bull, Merc, Mclaren, Ferrari and Alpine get +10.
It's why Alonso is always beaten by the Ferrari's and Mercedes in game and why Norris is battling Alonso most races despite a much slower car.
Yes, they're ridiculous.
Hate to keep repeating it but every time I see the topic brought up I need to say it:
EA, remove or nerf the boosts. They're making career mode horribly unbalanced and they have done for 4 years now.