Magic as intelligence only is pretty much held only up by convention but lets forget that for a second and bring up Dungeons and dragons. Here are all the stats in dnd that are used for it
1) Intelligence: Typical arcane study
2) Wisdom: Clerical study, empathy, and philosophy. Spiritualistic
3) Charisma: Self-sourced magic, you bend yourself and thus magic occurs
4) Constitution: Natural aspects of your physical body/form that are magical in nature.
The reason why Strength works for Polymorph is that it can be seen as something that "enhances" your current form. The stronger you are the stronger your form is.
Constitution and intelligence also works. And while Dex isn't immediately obvious there are indeed settings where shapeshifting definitely makes sense for dexterity (where it is described as physically contorting your form into desired shapes)
The point really is don't be so stuck in convention.
Glad to hear at least someone agrees with me
One thing I like about Divinity: Original Sin is that every stat is useful in it's own way regardless of what playstyle you have. Some stats are more important than others in certain playstyles but that isn't the point. Each stat does something unique that sets it apart from others. Generally, Dexterity is more accociated with Critical Hits, but I'm happy they did something different by making Dexterity a more defensive stat by giving a Defense modifier.
