You are completely wrong but hey-ho. The onus is on me to get rid of any Sunday i don't want to work. If no one covers it, I work it. Simple as. Plus many TOCs now have Sundays in the working week. Even at those few TOCs where they could do a 'bbq sunday' there's usually enough grabbers to work those Sundays.
Companies need to employ the correct number of staff. It is really as simple as that. Keep relying on people to do overtime and you get trouble. This arms race that your on about doesn't exist.
Even on London Underground, which doesn't do overtime except to cover late running or bank holiday working, weekend coverage is still poor. For a start schedules are compiled to minimise the number of weekend duties, then once you start getting rest-day moves to weekdays, domestic leave and most of all sickness, things are at the point when duties are uncovered and trains cancelled. Soon those who are at work get fed up with coming in to rubbish work, so the downward spiral continues. Even with the best management these things still occur.
I've seen and worked with various different ways of resourcing weekends, and have come to the conclusion it doesn't really matter how things are done, people just don't want to work weekends.
Paying a premium in whatever form does help get people in, but it still leaves the door open to things being volatile during periods where people particularly want to be off - summer, good weather, major football fixtures etc.