My pleasure.
PingYou was released in January 2017 and it says in the description
Development is focused on implementing features missing from the default xmpp client in SFOS
So adding XMPP-contacts was a “pain point” almost 5 years ago and it still is, so high time Jolla added this feature!
I should probably have added it to my Feature Request Support encryption, file transfer and groups for XMPP/Jabber.