You can choose to rent your cards or play them. Obviously you will do what is best for you at each time you want to make that decision.
Switching between both those has a cost. If you have 100 cards you are playing, then its 100 DEC each time you want to go from playing to renting. That's about 7c ... I don't know how much you get from renting but if its not at least 7c then its probably best not to rent.
Obviously there's a cost to the game every time everyone makes a transaction. In the past they didn't charge anything and it was abused. People found loopholes and listed millions of cards many times each day. In other words humans used tools to find ways to get every penny out they could and didn't care what happened to everyone else. This will make things more fair for everyone, including you. It will make using the resources of the team more rationale and thus people will only do things that are "worthwhile". Contrast that to the fact that people exploited things when everything was free to do.
Definitely I agree with you in this, the cards I rent out is max level and I play with them as well. I'm not a big player but whatever I play is max level. Definitely it's more than 1dec per card but since those cards also don't get more than 7-8 Dec per day average, my revenue is obviously impacted by 15%
That is based on the rental rates after this change, which of course might change as you reduce supply of cards overall on the market. Plus on top of that remember that land will start to use up a ton of cards as well.
And the second point is you don't have to pay the 1 DEC per listing each day. You only pay it one time as long as your cards stay rented. So you might keep them rented for 3 to 5 days, which will cut that cost down as a % too.
Maximum I put for 3 days, usually 2 days because that much space will make me miss champion league or wrong days