Thank you for that info. I have just checked for pulseaudio related packages - not the window manager - and frankly - I didn’t expect a window manager to be depending on a specific type of sound library 
I am not a KDE user so the dependencies of KDE is not familiar to me - but I can confirm this from a quick view on kwin dependencies.
When kwin has a hard dependency on pipewire then this is not a decision taken by Manjaro but a choice made by upstream KDE.
Changes made by upstream KDE is their choice and not a Manjaro choice - Manjaro just takes the fall.