This was quite the opposite for me. Main reason my wife and I used XMPP for several years was because Conversations was the only app to get timely notifications

This was quite the opposite for me. Main reason my wife and I used XMPP for several years was because Conversations was the only app to get timely notifications on both googled and de-googled Android. And this worked until at least Android 11. At the time, Riot.im (now Element) either drained my battery checking for notifications without Google Play Services, or seemed to work fine, but did not get notifications in time even with Google Play Services. What you're describing also has been true for iOS for a while. Apps cannot do long-polling and require a push notification server (usually provided by the app maker, e.g: siskin, snikket, chatsecure), and that adds another point of failure.