http://www.gamesas.com/topic/1342463-complete-character-design-freedom-damage-resist-caps-and-ridiculous-damage-thread-10/ did a great job compiling a good bit of information from other testers when the game released. Although he continually slaps the face of the franchise with the use of the term "mana", as that is another game entirely and not part of the TES world, it is still a well detailed wealth of information. This is part of the segment on Destruction and how effective it can be with or without the use of Alchemy.
At a base damage potential of 235, it is on par with the damage output from a developed 2H weapon. Then when you add Alchemy to the mix, it excels at 615.
The major difference, other than sneak attack bonuses, between Destruction and weapon damage is that Destruction is capped while the oversight of allowing Smithing to continue to allow weapons to be improved beyond Legendary is allowed and remains unhindered.