First of all just to make this clear that, this is not a guide. Sadly Dena has made this a P2W event where it is nearly impossible to achieve S Rank (i.e. within 6,000 rank) if you are f2p.
This video is rather beneficial for people like me, who is not a whale, but also spending for paid gems mainly for daily pulls. This team composition, along with the move sequence employed in the video are in my opinion the most efficient method to maximise the reward points.
However do note that I have only 2/5 Metagross EX and 1/5 Zacian, hence my goal is to solely achieve A rank (below 12k rank), and obtain the 5* move candy to 3/5 my Metagross.