Pre-Thameslink upgrades and pre WFH being a thing I used to commute every morning from Durrington to London Bridge which was due in at something like 0823. I think it arrived on time about once a year. There was a somewhat 'eccentric' man who had the timetable committed to memory and when the ticket's were being checked he would ask why, for example, the train was 6 minutes late into Burgess Hill.
He took it to the Nth degree but he did have a bit of a point. If there were no reasons such as weather or points failure, etc. trains should be arriving on departing on time and if they aren't the timetable should be adjusted otherwise you get circumstances where you have a train not ariving on time for an entire year like
this.
In fairness I recall Thameslink recalibrating trains after a while of running with the new upgrades.