Although what you suggested is feasible BUT I think this will limit/decrease your chance to get the Mythic card that you want and also it may not coincide with event Mythic card.
e.g. Light "Yellow" event going on and you have different color Pack in Colosseum event other than Light - then you cannot get event Mythic card from Pack, reducing the minor optional chance benefit from parallel running Colosseum event to finish event goals faster.
I think it would be great if lesser rarity Packs (other than Mythic at Top 5 Dally event ranking) can be earned at lower Daily rankings.