Apart from the minimum 1 DEC rental price floor having to apply to the season rental cost and not per day for this to make sense, I think this completely eliminates the "I want to give this card a try" option.

Imagine a player who gets completely demolished in a couple battles by a certain summoner or card and said player thinks "this card is so OP". Often it is enough to play a couple battles with the card yourself to realize its weakness (unless it has none like the truly OP cards 😉 ). This option is simply gone and instead you are force to either live with the mystery or you rent the potentially very expensive card for a whole season.

I think a good example of this would be a Akane + Venka which kills you in turn 0. Currently this would be 250 DEC per day, so 500 DEC to give it a go, seems reasonable. But to rent it for a whole season is already quite steep.