Let me replay the two scenarios, and see if I can unscramble my brains.
Scenario 1: The video that I screen-recorded on Android is sent over WhatsApp to iPhone. Plays out of sync. I assume fault is video-compression by WhatsApp on Android. What you are saying is WhatsApp on Apple was at fault in replaying the video.
Scenario 2: Video screen-recorded on Android is sent over bluetooth to iPhone. I forward said video from WhatsApp on iPhone, and it replays fine this time on both platforms. My conclusion is WhatsApp on iPhone works while the Android version is having issues. What you conclude is the opposite. WhatsApp on iPhone is flawed while WhatsApp on Android ‘just works’ because it can play videos made on either platform.
I think there is one way I can prove which conclusion is correct. I would have to replicate that screen-recording on Android, share it over WhatsApp on Android, and check if that video plays well on some other platform, like say Windows. This is assuming that WhatsApp has not, in the meanwhile, fixed the bug that caused the video to go out of sync.
Wait a minute. Even if the video again misbehaved on iOS and Windows, you could argue Apple and Windows are at fault, while Android just works.
I give up. I’m not that much of an iPhone fan to take so much trouble to prove that iPhones just work. So let’s agree to disagree, and thanks for the mind boggling.