Doesn’t your wording here clarify why using ‘fewer’ might actually be incorrect from their point of view? You’re referring to changes that are qualitatively larger, just like TFL may have been trying to communicate changes that are qualitatively smaller, routes with less noticeable changes to a smaller number of riders, or even a smaller number of rider-trips, without having to include an explanatory paragraph. The number of changes might be irrelevant to most people, and it’s a good thing if TFL is trying to tell you whether statistically you should expect to notice changes based on your usage, and not whether the potentially somewhat meaningless total number of changes is lower.
‘Least’ is a word that allows subjective interpretation, while ‘fewer’ is not. Saying ‘fewer changes’ implies something more specific than saying ‘least changes’, and in making it more specific it may literally communicate the wrong thing.