So I am taking a short break from studying now, your post will be a great distraction.
I generally agree that it shouldn't be too easy to earn card upgrades and being spammed with rares will kind of take the thrill out of the AH imo.
Yet you should consider that we will lose our cards from time to time due to server updates - so right now I think it's a great way to take the edge off, how frustrating would it be grinding for weeks to just start from zero the other day?
Furthermore I think it should be possible to earn the card upgrades not only by doing rPVE or only by completing campaign missions, just like the players have different preferences, the looting system should be just as flexible.
Back to the idea of earning cards by missions - these cards wouldn't be worth as much in AH anymore and idk wether I like the idea or not. It could also affect their rareness: if you could earn a rare card just by completing a mission it would technically become a common card - like moon, wasn't it a legendary card even?
I am absolutely pro mini booster packs, especially if it is that easy to get rares atm.
Btw: Do you use a strong Internet connection? I was figuring maybe some people (like me) won't get into the game because of a low data rate.