Why does Rainbow Six Siege stutter during rapid flick shots?

I felt my immersion shatter during intense flick shots when frame times spiked from 3ms to 18ms, which is lethal in competitive play. I tried enabling High Performance mode in Windows Power Options, but while clock speeds rose, the stuttering frequency actually increased. I then used the GamePP Resource Scheduler to set the game process to Real-time priority and capped background services at 400MB. Confirmed via GamePP Analyzer that frame time fluctuations converged to 5-11ms, with memory stable at 46-52℃ per AIDA64.