The Wii U had like two full E3s before it was released.
Meanwhile the Playstation 4 and even XBox One were unveiled 6 months prior to launch and both have solid to great sales.
Nintendo's issue is not when they launch, it's their overall product execution. The Wii U has tons of time, and it still bombed.
Honestly I don't think even Nintendo themselves deep down expects to make something that will dethrone the PS4.
What likely is happening is they have to replace the 3DS this year, and since NX is probably a unified platform, that means effectively it replaces both as a product line and that's A-OK for Nintendo since the Wii U has sold like hot garbage anyway. So they can't the "must do" out of the way in replacing the 3DS, and replacing the Wii U is just a nice bonus.
