Thanks for the feedback everyone.
My current saddle has an Evolution tree. It adjusts to your horse over time. Two of my friends have the exact same saddle, with the exact same tree and they tried to put mine on their much wider quarter horses and my saddle wouldn't fit. So I have proof that they do adjust.
And obviously my much narrower Arabian didn't stretch hers out as much as their quarter horses.
My current concern is that my saddle will not fit my arab/paint yearling Maverick when he's ready. He's almost as wide as my mare Amira is now.
And if I'm going to get a second saddle I was thinking of some sort of endurance type saddle since I already have a trail saddle with a horn. I love my saddle, so maybe I'll look into one of the endurance models made by the same company instead of the Abetta.