The 2 (or 3) slot chest inventory is too limiting for new players. A player could get “lucky” and get 2 gold or Ruby chests quickly and suddenly can’t play anymore.
Finding high rarity chests should always be exiting, but the limited space can make high rarity chests feel disappointing, as “I guess I’m done playing already. Might as well look for a different game to play.”
I understand that more slots become available later, but it’s new players you want to convince to keep playing. All the slots should be available for storage immediately, but players can only send missions on a limited number of them.
Minion rest time is also extra punishing for new players. Once you’ve collected a fair number of minions it’s not a problem, but if a new player gets “lucky” with 2 diamond chests now they can’t play for a day, and once they can play it’s only for a short period of time before they have to wait another 2 days for their minions to finish resting.
Players should always be able to send a mission to open chests without minions, and minions just add bonuses.
TLDR: High rarity chests should always be an exciting find. Currently they are often a disappointing find to new players.