So basically what you suggest is turning reward cards into a web2 version of the game. I mean, I would like to see that but with ghostcards not with reward cards.
What do you think about the limited unlock amount I suggested in my other comment. I think that is a good in between, where the majority can just use them as soulbound rewards, but if you put DEC into a share of the card value, instead of infinite print, you probably have the best of both worlds.
My view is that Soulbound Reward Cards = Event Dropped cards. Like playing RPG games, these cards are event items and only can be attain by playing the game/event. So I guess it is sorta web2 version of it.
As for ur suggestion in the other comment, I lack the economic understanding of how it would effect the ecosystem. The only scenario I can picture myself doing is purchase all those soulbound summoners and 1 or 2 OP card like KULU mastermind at MaX level for my BOT account in Wild.