If you have one wallet then you have a 50% chance of losing at least some coins and a 50% chance of losing all coins.
If you have two wallets then you have a 75% chance of losing at least some coins, but only a 25% chance of losing all coins.
So with multiple wallets,, you chances of losing some coins increases, but the chances of losing all coins decreases.
If you have one wallet saved on 4 different cards and one goes corrupt, you still have 100% of your coins.
So as long as you have a good number of backups, everything is fine.
That is an excellent point. A backup reduces your risk.