Indeed, renting out cards can feel like a full-time job always having to adjust prices based on Supply/Demand/DEC Price Fluctuations.

It's going to be interesting to see what they come up with for Chaos Legion. Based on the 20x Reward card prints I fear the worst with the market being flooded with new cards while there is nowhere near enough of Demand. I am quite confident that all the current cards will become very rare over time though.

In the end, it all is a game that will always require new and more players to come in in order to sustain the prices with in-game assets only going up and up in numbers. Something they could do is set a time-lock in the starter cards that someone who gets a summoner's Spellbook buys. It limits what bots that just want to grind rewards with that can get and anyone who hasn't started to build their own collection months into it I would say is not likely to do it going forward. So far the devs have quite a good track record coming up with new things to solve any issue related to the economy which is where all the focus lies. My main fear is that once rewards come down eventually which is bound to happen, nobody is going to be left playing the extreme pay2win gameplay.