This is what a rivalry should feel like. But as Tiger337 alluded to, we have not seriously fought the Clevelanders for any pennants or divisions for our entire existence, save the last couple of years. As a rivalry, it's just getting started, but I don't think we are quite at the boiling point just yet. We do need to beat them at some point for a division title or playoff series win, because rivalries have to be even, like Michigan-Ohio State, and not one-sided, like Michigan-Michigan State was from the 70s through the mid-2000s.
You know when it becomes a true rivalry? When it gets its own Wikipedia page, like this or this or this.