[2021] I do love the matchmaker in this game

Premium vehicles have the same matchmaker as every other vehicle.

There is no "rigged" premium matchmaking.

Likely the BRs of the lineup you were playing and the time of day. It hasn't "changed" because it never existed in the first place.

All of the details of how the MM works can be found here:

https://wiki.warthunder.com/Matchmaker