Casters had a series of debuffs, then melees and ranged have had a series of buffs (DH, DL, better weapons and gear). It's possible that after the 1) Caster level nerfs to spells, 2) Damage nerf of over performing spells (DB went from a slightly roided acid well at 2d6+20 to a slightly stronger AOE polar ray), and 3) nerf to spell damage in high reaper, that the 3 damage types were close together performance wise.
Unfortunately, a gap has grown since then with the 15 updates since. I've said it before in another thread, but the last expansion I felt had direct support for caster was Isle of Dread with the different spell damage boosts on gear (which along with green steel is the only good source of it in the game). I'm hoping the new Loft stuff continues on that (since they said crafting would be similar) and gives casters some of the new toys that other builds have been enjoying.
Insert rant of my own, which I've lamented to guildmates at length, about what classes/builds are supposed to do. DPS casters were largely glass cannons, huge firepower but with limited spell point pools and lower defenses. They were limited by distance (no sniping from across the map like bows), forced to the midrange position where they had to be on their toes to avoid accidental annihilation. And that was fun, that was the caster role, to be damage on the edge of the red zone. But now they are more of a glass flintlock, only doing decent damage against higher and higher pools of hitpoints (and even then that decent damage is only by geared out toons with the hard to get gear I mentioned above). Even if they reversed all the nerfs I mentioned, I'd be surprised if I could match much less beat the DPS of a geared modern melee or ranged toon, and even then I'd be keeping an eye on my ever diminishing SP.
Now, my opinion on melee/ranged should be debuffed or if casters should be buffed. I'm on the side of caster buff instead, as the difficulty of content has grown since the nerfs. If everyone was doing 80k+ a second and LoB was the highest raid (boss with sub 4mil hitpoints), then I could see a nerf to reduce damage (not to the point of casters being top DPS, more on pair with the spinning melees but still weaker than say single target DPS like throwers/bows). Since we are not in that era and instead are facing mini bosses with 2-10mil and raid bosses with 60mil+ pools of hp, instead of making everyone suffer I'd just like a boost to be able to play with the big kids again.
Rant over (reserve the rights to edit this post + respond to other comments/opinions)