If you're just going to make attribute effects map to abilities and add new abilities, I don't really see the point because you're just putting points in, and if you're going to add the effects attributes give on to existing abilities, then it definitely seems like you have less freedom to me. I mean, maybe you could ditch strength requirements on armor and just use armor specialist, for example, but that's not particularly interesting to me either. And I'd rather see interesting ways to synergize water and fire together instead of making them even more exclusive. Though I do think mages should get a benefit for focusing on a particular tree that compares with investing in multiple trees.
The way I see it, dexterity might reduce global cooldowns and make you better at everything, but only by a little bit. You're still going to have a limited amount of attributes, so you'll have to decide if you value range, cooldowns, or +status application, with my examples. Different builds would value different attributes, but, say, a damage-focused mage could invest a lot in strength and dexterity to increase range and decrease cooldowns, where a cc-focused mage would invest in intelligence to increase the chance for statuses to apply. Likewise, a ranger that wants to hit enemies from really far would need a lot of strength. Probably Larian would keep primary attributes to some degree so a mage would still need at least a little intelligence to be effective, but it'd be nice if the requirements were a bit looser.
Another idea for intelligence is if it let you learn more skills per ability tree. Say, 5 int over 5 = 1 extra skill.
