Couldn't really have put it much better myself.
Buff cast speed to how Ace was and tao's will be soloing everything unless you heavily nerf other aspects of the class which - in my opinion - is not a good idea because you'd be removing intuitive aspects of a class just for them to be able to cast a little bit faster. The class is FUN at the moment and pretty well balanced in all aspects. You've hit a good spot, why ruin it?
People think they're going to roll assassin but when they realise that a level 42 warrior in full dc kit can 2/3 hit them with TDB, they'll start to realise that all that early game/utility maybe isn't worth it - and thus you'll get more variety. People can only decide from what they've seen on streams, this is why Open Beta is a better idea as it properly gives them an assess-ability of each class from their own personal experience. Take KENPACHI for example, he and I were watching streams and were convinced assassin was the class to go, but having gone assassin myself just now and him warrior, we're soon realising the warriors slowly out-scaling me due to the massive health pool and TDB power spikes. All he needs is a bit of a.speed, and he's pretty good to go. Simply playing has changed his entire aspect of the game for his beloved class, and we realise that it'll actually take a warrior and a sin to take down the serious bosses due to the sin being able to lure it safely, and the warrior being able to take more of the hits. Then you'll probably want A) a tao to heal you / buff you / assist you in any way shape or form as tao's do and B) a bunch of wizzies to get you to said boss safely and rack up some exp along the way.
The only class I think doesn't fit this niche, is the Archer. I've yet to fully understand their role in a group hunt - just more single DPS but ranged and a bit of utility? who knows, that's next on the testing list. Point being every other class currently fits a niche and is useful right now, and, dare I say it, balanced.
Buffing cast speed is not the answer here unless you can buff certain spells only (to my knowledge, not possible) as it effects wizzies positively too, and if a wizzy can cast even faster then you're going to have serious issues late game when met/blizz/ff comes into play. Buffing cast speed horribly imbalances the PvP which... is a terrible idea.
Yes Curse is undeniably broken, and should be on a huge, huge cooldown for a mass-aoe anti-fun spell that cripples everyone in range - but I expect that to get balanced. But I respect your opinion, even if I disagree with it.
In the end it's up to Samuel to decide how he wants his server. I think personally he's done a good job with the classes so far, despite what the moaners are saying. All that's left is to test late game more extensively, and start balancing from there.