@gyl_xyz Your observations absolutely are correct. I don't know the complete internal details on how communication between Appium and UI automation happens.
But when you use AccesiblityID, appium creates UIautomation script and sends it to UIautomation. However in the case of XPath, Appium gets the complete DOM> process the XPath you have provided> creates UI Automation script > sends to UiAutomation.
So because of these intermediate processing, it takes more time compared to AccessiblityID.
So my point over supporting XPath to the people think XPath is bad
1. Don't use XPath, they are pure evil, Stop everything and keep whining to Dev's to provided proper locator.
2. Use XPath, Whenever you feel necessary. Complete your task at time.
Anyway i said too much, @gyl_xyz thanks for pointing it out