I was confused by part of your post until I discovered that "shard shop" isn't a thing I have access to since I don't have anything above 5-star
Also, as far as the main currency - is it still the case that it's better to spend it on level/energy refreshes to farm specific guys than to buy chromium packs? I have over 3,000 apparently so i am curious if that 8 pull with a guaranteed character is worth a shot.
It's better to use it for refreshes for sure as those packs really don't seem worth it normally but hey you could get a good pull! They are fairly free with the currency giveaway so, if you've got it and you wanna give it a try, might as well.
I've bought a few smaller packs when they gave out sorry money for downtimes and stuff.