Where exactly are you noticing thinness and decreased quality? Hairlines are not perfectly symmetrical in most people. Hair can also grow differently on each side of the head too. Your hairline seems ok and there’s no obvious signs of miniaturization in these pics. Without any “before” pics we cannot determine if anything is happening.
Take addional photos of the crown and vertex as it currently is. Then take all the same exact pics (lighting, hair length, camera angle etc) again in 6 months and compare. Repeat the process every 6 months or so to monitor the situation.