There is nothing good about this.
You need to buy KCS in order to be able to buy bitcoin with that discount.
They are basically paying for you to buy their shitcoin and pump its value.
This is moral and ethically wrong, and also has consequences for KCS holders. Additionally, some questions naturally shows up: is Kucoin really safe? Do they have the liquid to withdrawal all that btc with 90%?
They shouldn't be doing that IMO.
I don't see how is this thing wrong. This is their way of promoting their KCS token and thanking their community in supporting them. You buy KCS, then you buy their BTC with your KCS, if you already have KCS it is a very good deal. Besides, purchase amount per verified user is limited. They won't do this kind of promotion if they do not have BTC in hand else all their effort will be in vain if they failed to deliver those BTC.