This was not Hamilton deliberately slowing down his pace to allow Qin Miao to catch up. Even though Hamilton had enough time to catch up to Verstappen and overtake him, this is a race. Even at his peak, Hamilton wouldn't arrogantly believe he could take first while helping Qin Miao to secure second in an F1 race.
Although Qin Miao had secretly done this sort of thing in F2, that was just F2 after all.
Qin Miao being able to keep up with Hamilton's pace was purely due to his own strength being strong enough. Plus, the team had just informed Qin Miao that his tire degradation curve was slower than expected, allowing Qin Miao to slightly increase his speed, and after knowing Hamilton had pitted, Qin Miao had charged up his ERS for a long time, using it all at this moment.
Although there actually seemed to be no need for Qin Miao to chase down, since no one in front could be reached and no one behind could catch up, he could just coast for the last few laps.
