Easier to understand maybe comparing to this chart instead?
https://www.fanatics.com/mlb-jersey-size-chart/x-6031+z-87973170-2468593456 If that's right then by body width their M is about M, L is little smaller than L, XL is a little bigger than L, and 2X is a little smaller than XL
By length the one size up rule seems to work except 2X is longer than a US XL
All the sleeves are a bit longish in comparison