I "grew up" using my dad's 18.5" but never learned how to properly use it. Everything was wide open, direct and meat was tough. The 22.5" makes things like indirect cooking and more sophisticated techniques more intuitive because you can see how it's gonna play out. That, as much as its extra space, make it far more versatile.
I still have dad's 18.5" and have learned how to use it but can't as easily make it do what I want, but partly that's because the daisy wheels give me fits--only work for a few cooks and then become clogged with grease or bent. So it's my 2nd-string utility player. In some ways I like the Jumbo Joe better because the need to create distinct indirect or direct zones is absolutely paramount there due to how much closer the heat is. Irony, that.