Isn’t the week of episodes just the first part? Sure I’ve read (maybe here but I’m too lazy to check back) it then returns in the new year with a live show element.
No just the four episodes with a live final on the Sunday: https://www.itv.com/presscentre/ep4week51/x-factor-band
I wonder who determined how many/few episodes the series would have? Sounds rather like damage limitation from ITV, especially after seeing how badly the celebrity series was going.