No offense, but the whole, "Brawl will sell more in the long term" is a bunch of crap. No matter how well the Wii sells, Brawl can't even begin to touch Halo's strength.
Halo sells somewhat well in Japan, and Smash Bros has never been amazingly strong in Japan, although it does sell quite well, and manages to have long legs.
Super Mario Galaxy, maybe. Brawl? No chance.
Halo's strength? Well, let's take a look at that shall we. First, I'll paste the numbers for some quick reference:
Super Smash Bros Melee outsold Halo.
You said Halo sells somewhat well in Japan, and Smash Bros. has never been amazingly strong in Japan, but that's just freaking ridiculous. 110,000 units is not somewhat well, it's complete shit. 1.44 million units is amazingly well. Lets look at some other games that have sold less than that in Japan:
Kingdom Hearts 1 and 2 sold 1.16 and 1.24 million respectively.
Metal Gear Solid 3 sold .86 million in Japan.
Everybody's Golf 3 sold 1.39 million in Japan.
All of these examples were on a system with more than 5 times the userbase of the Gamecube in Japan. There were only 4.02 million Gamecubes sold in Japan in it's lifetime. That's a 35% lifetime regional attach rate, which is nothing short of incredible. It's ridiculous to not say that's amazingly strong.
Now lets move on to the total sales. Of course there is the looming beast of Halo 2, which managed to outsell Super Smash Bros. Melee by 1.69 million units. This sounds like a lot, but lets break it down a bit more:
Super Smash Bros. Melee was released on the Gamecube as a launch title. This means that all of it's sales were based off pretty much nothing but its legs. It powered it's way to the end of the Gamecube's life with strong legs.
Halo 2 was released on the Xbox on November 9th, 2004. Prior to it's release, the Xbox had sold 17.34 million consoles according to the latest fiscal reports (filed in September). So, with 17.34 million consoles, Halo 2 was able to pull off 2.5 million units sold in it's first week in America. In the next 3 weeks Halo sold 735,000 followed by 377,000 followed by 293,000 units. Within it's first month on the market, Halo 2 had sold more than half of it's total lifetime sales, again on a console with 17.5 million units already out there when it launched.
The Gamecube sold 21.59 million copies worldwide in it's life. The Xbox sold 24.76 million copies in it's life. This gives Super Smash Bros. Melee an attach rate of 30.5% and Halo 2 an attach rate of 33.4%. Not a whole lot of difference when you look at it like that is there? Oh, and remember, we are talking about a launch title vs a game that was launched when the Xbox had already sold 75% of it's lifetime sales.
In review, you are saying there is no chance of Brawl surpassing Halo 3, when Melee already outsold Halo (a fellow launch title), and barely did worse than Halo 2 in lifetime attach rate, when Halo 2 was released 3/4 of the way through the Xbox's very short life. To add to that, Halo 3 is being released on the 360 when it has only sold 11 million units worldwide, wheras Brawl is going to be released on the Wii (if sales remain the way they are) when the Wii has sold 14 million units worldwide. The gap between the systems in sales will continue to widen throughout their lifespans as well. Considering that Smash Bros. is a series with huge legs, this can only benefit it, and can only hurt Halo, a very top-heavy game.