I have a question: why do they make the cool down rule affect ranked battles as well? Is it because you can also earn real SPS in both ranked battles and survival mode, or it is because they just want to create a form of excitement by making it harder to play a card you've already played in maybe modern or wild?
I think this new mode came about to give new use cases especially to cards that are out of modern, cards that systematically lose value when they leave the Modern Format.
The cooldown mechanism adds more emphasis on strategy because losing is equivalent to not being able to use a card for a period of time that is very long for common cards.
In the new format, legendary and gold cards have much more utility precisely because they have a lower cooldown ;)
Survival Mode is interesting and fun but my main focus will always be on Modern Format because it is the only ranked format where there are no bots.