I can sympathize with Ari. I was also in a "balance is all important" phase a few years ago, and boy, is it hard to break out of.
To me, balance is one of those bugaboo concepts that has some great positive uses and connotations, but carries with it problems all its own. Its a positive aspect for game design in that everyone at the table wants to have fun, but if one character is more powerful than others (whether due to a class, feat, spell, magic item, etc), it often leads to resentment and problems at the table. By controlling some of those options and keeping some wahoo ones reigned in, the game is better for everyone.
On the flipside, being worried about balance all the time does take a toll on creativity. There were several times when I was DMing 3e (which was the time I was most concerned with balance) that I had a cool idea for a spell, critter, magic item, or whatever- but I just couldn't quite figure out a way to make it work in system and be balanced. It was frustrating as hell.
For me, my balance revelation came about three years ago, while I was running a WHFRP2 game. Now, WHFRP2 wasn't the most balanced of games, and some PCs are more powerful than others, but there are also some mechanical and roleplaying hinderances to that power (chaos manifestations when using magic and people's attitude towards magic being the big two). Coming into the game, the players knew wizards were going to be powerful but that was also a steep price to be paid for that power. In contrast, D&D over the last 10 years has really tried to eliminate ALL negative consequences of magic and power, whether mechanical or roleplaying in nature (which I do think is a mistake). I've found if you're up-front with players about there being a cost for greater power, whether its mechanical or roleplaying in nature, they are usually ok with it, as long as they are aware of the repurcussions beforehand. Once players understand that, then the overriding concern with balance can be relaxed, and creativity can start flowing again.
My solution for my 4e campaign was to make arcane magic risky, and subject to spell failures on rolls of a 1, as well as having many people in the world suspicious of arcane casters. Warlocks don't tend to suffer spell failures quite as badly as wizards, sorcerers, bards, or swordmages do, but they are also beholden to other entities via their pact. Divine characters have more RP restrictions- they are subject to the dictates of their religion, with certain holy days they must observe, taboos to avoid, and divinely-granted visions their gods expect them to follow up on. Primal characters must commune with spirits for guidance and power, and can easily offend them by engaging in activities that are contrary to the desires of the spirits. The payoff? A houserule allowing all arcane, divine, and primal characters to use healing surges to deal extra damage with powers, or to immediately cast a ritual, or to manifest various non-statted, off-the-cuff game effects that would be cool in play (thematic or dramatic in nature mostly). Martial classes don't get those bonuses, but they also don't suffer the restrictions. When I told my players about this, they LOVED the idea, and have been just fine with some of the classes being a little mechanically unbalanced due to the costs associated with the power, as long as they know about it up front. The other nice thing is I didn't have to do a thing with the Character Builder to allow for this to work.
As a DM, I found that its best to not even think in terms of game stats, powers, etc., when designing monsters, encounters, and adventures. Come up with the idea first, then make the stats fit it relatively closely. If the ability or critter is a little overpowered, thats fine- PCs are usually much more resilient and adaptive than most DMs give them credit for, and can often deal with many situations that seem hopeless. And hey, if they can't, then running isn't a bad idea!
Now, Ari is in a slightly different place than most of us, in that he's writing professionally and submitting his work for public consumption. WotC does have an obligation to turn out quality material that won't wreck the game, and from what I've seen, Ari's 4e work has been the best I've seen from him. I'd say this to Ari- we're our own toughest critics, but you really have nothing to feel bad about. I personally think your recent stuff is your best, and is plenty creative. My advice to Ari would be this: take some chances and do some crazy stuff in your home game- just see what happens. As you get more comfortable with being "unbalanced", try some proposals to WotC and see if they bite. Who knows, you might be writing the 4e Unearthed Arcana!
