Both the A220 and 321XLR are delayed. A321XLR Certification was an issue, now its engine problems on the existing fleet. The fuel tank issue that delayed certification cost 2,500 kgs to fix, so that sounds like an hour less range.
I was speaking with customer service staff in MEL a couple of weeks ago and they revealed that they have been told that most flights there will eventually be A220s.
in other news, QF is going to mod the oldest 737 airframes* to install fuel tank nitrogen inerting, which is not required until 2026. So we are going to have those pieces of —— for a while yet.
*.except the first two, according to the engineer that was laughing/crying about it.