Regarding the Master Rank Matching System

This is just my speculation, but is the reason Diamond rank players are included in Master rank matching not just to make matching faster, but also to balance the difficulty between regions?
If this is to eliminate regional disparities, I would recommend setting rankings by region so that the number of people who can become Predators changes in proportion to the number of people in the Master rank.　In other words, since your rank is determined by region, you won't be able to change regions to easily raise your rank, which is a good thing.
The downside is that you won't be able to speed up matching by automatically changing regions. However, this automatic region changing system forces players to play with high ping, which is not a system that allows you to enjoy Apex, so it's unnecessary and not a problem.