I agree with and understand the logic and changing to numbers is just an early integration with SkyTeam priority but I don't understand why Star Gold is in Group 1 and why EuroBonus Silver or lower even gets priority boarding.

It would have made more sense to restrict Group 1 to EuroBonus Pandion, Diamond, Intercontinental Business Class/intra-Europe C and Group 2 to Plus, EuroBonus Gold and StarAlliance Gold. This would leave your group 1 very small which is what other ST airlines do, your group 2 cleans out your priority boarding and then everything else just goes in Group 3+.