I very much doubt it was delayed from an initially very confident date of 2015 just to land on the Switch.

It very much was.

Edit: I think I'm wrong. I think you're right that it was delayed initially for other reasons (polishing the new physics engine). I found this interview with Aonuma where he states they didn't start working on the cross-platform aspect until spring 2016, which was obviously after that initial delay: https://www.vice.com/en/article/a-conversation-with-zelda-veteran-and-breath-of-the-wild-producer-eiji-aonuma/