Million Reasons is better left as the third single. She can perform it at the 2017 Grammy's around that time and then it'll be slightly fresher for the 2018 Grammy's.
For the people who are disappointed about Million Reasons, A-YO was the smarter choice for right now because Million Reasons is a definite hit and can be fallen back on in case A-YO underperforms. Would you want MR second single and then a potential flop third single and then the era ends? It was the right decision because it increases the potential for this album to have longevity.