This is a point against your argument, not in its favour. The percentages of users who use or don't use specific features, in isolation, cannot be effectively

This is a point against your argument, not in its favour. The percentages of users who use or don't use specific features, in isolation, cannot be effectively used to determine those users' opinions on the relative merits of those features. There are so many other factors at play that you really need to do some kind of explicit survey to determine whether, just as a for instance, some of those 65% would prefer a different way of saving files but don't have the choice (or think they don't), and, conversely, whether some of those 35% would be happy to use that feature, but don't know about it.