Yea, I know we all want Zelda as soon as possible but I think this is the better strategy for Nintendo. The Switch will have good sales at launch due to 3D Mario. Zelda will hit in June and add to the momentum. Compare that to the Wii U and it launched fine with New Super Mario U, but quickly lost momentum because there weren't enough releases after launch. Zelda will ensure that doesn't happen on Switch and will help it gain momentum.
Edit: Of course they need to have some games ready for holiday 2017 but that shouldn't be an issue I hope.
Yes! 2017 is aiming to be leagues better than Wii U's first disastrous year. The fact that even Mr. Iwata (RIP) had to apologize for the lack of games on the first semester of Wii U was very depressing. But it seems Nintendo has now learned from those dark times and they have the whole 2017 covered to keep a steady lineup of games through the year without droughts. It will help even more if 3rd parties keep supporting the console through the year and not just when it launches in March.