Disagree with the tier-based change.
IMO, every 10 rounds, WGT should generate a stat block, and you should maintain 5 stat blocks. When the 6th is generated, the 6th oldest stat block will be discarded. For example:
Last 10 rounds (stat block #1) GIR: 85%
Stat block #2 (rounds 11-20): 75%
Stat block #3 (rounds 21-30): 90%
Stat block #4: 80%
Stat block #5: 85%
Stat block #6: 75%
Stat block #6, being the oldest stat block, would be discarded as soon as the new #1 was generated. Once you had 50 games together, this would just continuously throw away your older games, making your stats based completely on recent rounds, not your past 500-2,000 rounds.
Stats also have huge problems outside of this, and all of it would be incredibly easy to fix.