No, the reason this fee seems outrageous is because the original poster paid 5.6% x 7 = 39% to short overnight.
As previously noted Tradezero clearly state on their website that they charge "7x market rate cost for 1st night."
https://www.tradezero.co/pricing
What I do not understand is why Tradezero believe that is a good business decision? Anyone doing simple research before opening an account - that is anyone with the potential to do real business - will stop and take their trading somewhere else when they see it on Tradezero's webpage like I did.
People who do open an account like the original poster will eventually find out this 7 x overnight charge like the original poster just did when they are charged the fee. When they do, they will stop making short trades and take their business somewhere else.
It's simply really bad business.