The choice to start on medium tires was mainly because the only person in the back group posing a threat to Qin Miao was Sainz.
Apart from Sainz, on a track like Monza, where overtaking is relatively easier, Qin Miao's medium tires would be enough to handle most drivers' defensive maneuvers.
Although Mercedes' car is lacking this season, it's only in comparison to Ferrari and Red Bull. Compared to these Earth-bound cars, Mercedes is still depressingly fast.
The later switch to soft tires was for a final sprint. By then, the fuel in Qin Miao's car would likely be running low. After getting the tires up to temperature, Qin Miao could consider using the soft tires to set the fastest lap in the latter part of the race.
After all, Qin Miao is still leading Verstappen in the drivers' standings and still has a chance to defend the title. The team also considered this point, combined with Qin Miao's starting position, and developed this pit stop strategy for Qin Miao accordingly.
