Thank you for thinking thru this. But can you also take into consideration of BCX too instead of just purely level? This will also justify those half lvl up cards.

Using your example but with BCX assumption

Level 5 Common (60 BCX)
Level 1 Common (4 BCX)
Level 1 Rare (2 BCX)
Level 1 Legendary (1 BCX)

Revised

Another Example

Level 2 Common (13 BCX)
Level 2 Common (8 BCX)
Level 1 Common (4 BCX)
Level 1 Common (1 BCX)
Level 1 Rare (2 BCX)
Level 1 Legendary (1 BCX)