When exists? was removed, it was roughly an order of magnitude more popular in Ruby code on Github than exist?. I don't think you can argue from the position of improved readability when, given the choice, it was what the majority of people expected, wrote, and had to change. This change in Ruby is pretty difficult to defend. It didn't really do much but break people without giving them anything in return. It didn't improve maintainability of Ruby itself, it didn't make maintaining Ruby code easier, it didn't advance any secondary goals to improve Ruby.

10 years is not an especially long time period for a software project to be maintained. There's a reason the Linux project is so emphatic that it never breaks user space.