Since those services all died off my memory is a bit foggy, but I recall stacking contacts in one with Adium & being able to prioritize in that meta contact which service they provided. But I really only ever used it for two-person conversations so I had no experience with the group situation. Even still, a multi-chat app was a vastly better user experience than running several independent applications (with the cost of missing ‘advanced’ features & occasional outages as protocols needed to be reverse engineered & the proprietary providers had no incentive for backwards compatibility).

> Google particularly abandoned it for really no reason

What most annoying is seeing Big Tech now trying to write a new standard to comply with the EU instead of using the existing standard they abandoned that already has all the mileage & scaling looked at. Instead all the same hurdles will have to be overcome yet again, just like the current growing pains of Matrix meanwhile XMPP is still quietly holding strong for massive chat/presence systems.