This may sound impossible to believe, but my players don't pick the best options for their characters. They really do role-play their characters. The player at my table who rolled up "halfling gypsy" as his starting occupation thought the character would end up being a Thief if she survived the funnel but since she had two spellbooks at the end of the session he said "She'll probably try so hard to read these books that she ends up becoming a wizard instead." This player doesn't even own a copy of the rulebook and has no idea how the magic system works, let alone how "cool" demihumans can be. I've been playing RPGs with this guy for 6 years and he's never owned the rulebook for any of the systems I've run, except for GURPS.
The other player in my group who doesn't own the rulebook rolled up an "elven artisan" and a Personality of 5, but he wants to play a Cleric because he thinks the concept of an inept cleric would be fun to role-play.
In short, the dictates of storytelling are more important than stat blocks for my players, so what is balanced is something I never pay attention to. That being said...
...you really need to ensure you give a seriously good incentive to playing a human. Possibly even to the point of tipping the balance slightly in their favour, because in a lot of players' eyes, the demi-human races have a cool factor humans lack, and even if mechanically balanced, that can still lead to demi-humans being selected more than humans.
Well, what I threw together at the beginning of this article was just me eyeballing the classes in the book and trying to make something cohesive and logical.
I would probably also dump saving throws and stealth, otherwise it's way more advantageous to be a nonhuman wizard.
I could see getting rid of the stealth ability, but not the saving throw modifiers. I see rolling up a demihuman race as a trump when it comes to saving throws. The random nature of character creation leave you with only a 30% chance of getting a demihuman race and then what are the chances they will survive the funnel? It's pretty random. I think keeping the racial saving throw modifiers makes them more special, it's like having Infravision. Any player who actively wants to play the stereotypical elven fighter-mage then has only a 1-in-10 chance of even getting to play an elf before they throw that character through the funnel. I don't think you need to make humans stronger to give people an incentive to play them for the same reason you can justify giving the demihumans a slight advanatage, there's a 70% chance you'll be playing a human.
But, again, my experiences at my gaming table are unique as I've already stated.
I'm more curious how other people would break down the demihumans into the traditional four classes.