Great analysis, thank you for doing all the math! I was just thinking that another related calculation which is relevant is the expected amount of chests(or time) it would take to get all reward cards to max for a league while playing in that league (e.g., how many silver chests on average it would take to get rewards cards up to a silver level). That would tell us how much play is required to get cards to a "playable" level.
RE: Soulbound Rewards Cards - Expected # of Chests Required To Max Cards - by league, rarity, and foil | Splinterlands