The game doesn't have the playerbase to support grinding PvP cards.
Anyone whos interested in PvP and joins as a newbie is going to be slaughtered in a PvP grind system and be instantly demotivated to play.
If we had 10k players on all the time that'd be fine, there would be plenty of other newbies for newbies to be matched up with. But we dont.
Realistically we have 500-1500 players on at any time, and we have to keep in mind a large portion of them will be playing PvE.
Locking ranked behind collecting cards is an idea i find pretty revolting, if collecting cards is a thing it should be the other way around, collecting for unranked, all cards free for ranked.