Sure, the rest of the week has some reliance on overtime, but it's not the same as a day (Sunday) where it is possible that 100% of shifts are reliant on overtime.
Yet Sundays have worked reliably for many years based purely on voluntary overtime (100% shifts covered isn’t as ridiculous as it sounds when there are far fewer shifts to begin with). The industrial dispute and the back pay etc. have brought things to a head recently. But there’s no reason why things shouldn’t go back to how they were.
Despite the government’s statement there are still no formal proposals to bring Sundays into the week across the board, as far as I’m aware. I’ll be staggered if they do that due to the cost, so more likely we’ll continue with largely the current arrangements plus a few tweaks.