I am all for minimizing the impact of bot farms, but I am a no vote on this proposal.
To me, there is no difference in renting or self delegating to a different account, so treating those two things differently is ill conceived solution. I also do not think CP is the answer either.
The more simplistic and effective solution would be that a card could only play for 1 account per season. Whether that card is owned, delegated or rented, once it is played, it is in cooldown for any other account for the remainder of that season.
This means that all rentals would effectively be season rentals.
This means that all delegations would be season delegations.
This would close multiple massive loopholes that allow bot farms to farm cheaply and other loopholes that allow top tier human players from shuffling cards to diff accts every few days, or renting for just a few days to push up as many accounts as possible to leaderboard positions.