1) The question 'Acid Orb needs something to be viable' is flawed. Acid Orb is not a person. It doesn't have feelings or a sense of fairness. It's a few lines of text in a book. It's not even the fictional depiction of someone who has feelings.
Moreover: Ranged 20 is its reason to exist. It's a fine, if not exciting, power that will make its way into builds with certain parties. Combined with a eagle shaman or a skirmishing warlord, it's incredible damage dealing for theparty. It's not for all sorcerers in all parties, but really, no at-will should be 'for all characters.'
2) The question you SHOULD ask is: 'Am I comfortable with characters busting out 1d10+30 damage opportunity attacks?' especially when said massive damage doesn't cost the character their normal striker damage in any way, shape, or form. As much as you can pretend otherwise, every sorcerer at-will is 'small dice'+'massive damage bonus' and you cannot pretend it isn't when balancing decisions like this.
The statement 'Cosmic Sorcerers get an area of damage around them' doesn't even factor in an argument, it's like comparing grapes to planets; the scale isn't even on the same level.