Are you talking about Wizards actually learning the spells, or using scrolls? Because I can tell you right now, that will probably 95% not change. Honestly I have no issue with it. I think the whole idea of scrolls is anyone can use them, but depending on your build, certain classes, with certain scroll spells will work better for them. For instance a cleric using a scroll heal will heal a lot better than a wizard using it. A cleric can use a firebolt spell, but it will not hit as hard as a wizard using it etc. I may have missed it, but I never saw where Gale or the PC as a wizard could actually learn cleric spells besides scrolls. If they can actually LEARN the spells, yeah I would be against that. But using scrolls? Not so much.
I realise I didn't make my questioning particularly clear but I was asking why Wizards can learn/cast Cleric spells and the next question should have been why can non-caster/magic classes use scrolls? I totally see your points on a Wizard casting a Cleric scroll but far less effectively, that makes sense and feels immersive. Is it the case in-game that if a Wizard casts a Cleric spell scroll that it's not as efficient? I'd be interested to see.
I mean it has in my experience. I don't have any numbers on it, but when my other classes try to use a healing scroll it doesn't seem to barely even work. When my cleric does, it seems to give a larger chunk of health. But I am sure SOMEONE has done actual numbers on it in here lol. It appears the same with damage spells.