There is another aspect to scarcity too, and you alluded to it with the Llama/Yodin/Kitty "opponent check", an individual card can be scarce AND high demand, a well know feature of the meta game ( Scarce in itself means.
nothing without demand, I have several 1/1 artworks stuck to my fridge :-) )
I'm undecided if this aspect of scarcity is good, on one hand it creates true chase cards, on the other it's a bit of a lock-out spec for meaningful play.
I mention it because , not only are cards proliferating but abilities are also growing, there is usually a plan B and C for any key card. I feel the size of the reward card set adds to the issue.
I like Black Foils, I think they should be rarer, I personally don't see the need for Arcane versions, but I'm not a collector, so I appreciate that aspect is lost on me.
YES...BRING LEAGUES BACK.....allow ppl to build a Bronze deck, work up to Silver, expand into Gold..... let ppl start small and grow, as it is now it is rather meaningless to have a "bronze deck" outside of Brawls and Tournies, it's very much a "go hard or go home" scenario, and I feel that new players tend to choose the latter more often than the former