Ok so lets stop you there.

1st - your comparing a game with a rating of E which appeals to a wider audience then a game rated M which doesnt so the attach rate will be stronger on a game rated for Everyone.

2nd - Halo increased its revenue by nearly half a billion dollars ($400m) on launch. MS and XBox arent worried at all.

3rd - Halo is already sitting on 2m without including Digital sales. It will most likely keep selling for years to come (or until Halo 6 comes out)

4th - Splatoon and Halo are two completely different games design for 2 different audiences.

5th - Halo is competing with the big fish in the sea like BattleFront, COD, Fallout 4, Just Cause 3 and many other FPS games that released around the same time period.

Splatoon is a great game and i play it with my Brother all the time, definitly one of the better games of 2015 however Halo 5 is better in my opinion and to many reviewers aswell (Halo 5 - 85 meta/Splatoon - 81 meta) Again both different games for different people. To me Splatoon is a casual fun kids game where as Halo is more for the Hardcore gamers. Apples to Oranges.

Also if i might add, if you think Halo is doing bad because its not outselling a new IP then what do you think of all the other FPS games like Sony's Flagship FPS game in Killzone?

Finially Spatoon isnt even a FPS and should be compared to games like Gears not Halo.

1st Its rated T not M.

2nd Do you know how high the expenditures are? For the ads alone... very high I think.

3rd Yes it will, but the sales are dropping at a massive amount every week. Lets wait for that.

4th Yes. But both games are shooters. Thats the point here I guess.

5th Many people said that Halo is one of those big fishes or even bigger. Fallout is a big fish too. Did it have problems? What about COD? Sure Halo is only on Xbox One, but look at previous Halo games. This should not be a problem for a game like this.

1st Its rated T not M.

2nd Do you know how high the expenditures are? For the ads alone... very high I think.

3rd Yes it will, but the sales are dropping at a massive amount every week. Lets wait for that.

4th Yes. But both games are shooters. Thats the point here I guess.

5th Many people said that Halo is one of those big fishes or even bigger. Fallout is a big fish too. Did it have problems? What about COD? Sure Halo is only on Xbox One, but look at previous Halo games. This should not be a problem for a game like this.

Not sure which country your from, Halo 5 is rated M here not T, different rating systems it seems. You also know Halo 5 will sell thought the years. Its getting more and more content and will probably stop selling until the next big Halo game arrives.

Dont forget on the WiiU there isnt much shooters to choose from, Spaltoon has nothing to compete with, so its User Base will more then likely consider buying Spaltoon where as Halo 5 is competing with just about every other FPS game in existent and its doing a fine good job at it. Halo doesnt need to outsell everything to be a successful game niether does Splatoon.

Lack of shooters on WiiU play for both sides.

If there was no shooters on WiiU before and there wasn't a huge influx of users then the userbase don't really care that much about shooters. So altough it doesn't have competition from shooters (but have from several good games) it also don't have a formed market on it. So you can nullify this point. It probably is selling more on it's freshness than on lack of competition.