You can guarantee that binance doesn't slack when it comes to security, it just happens that the hacker is extremely skilled and has enough patience to execute his/her plan. With that said, Kucoin, like any other exchange will have some kind of security flaw that would only be revealed if it caught the attention of a skilled hacker. It really doesn't matter what you choose to use.
There is no exchange that is safe in this market and it can be attacked at any time if there is a major flaw from the development team of that exchange. I think raising security is necessary and we need to have insurance when participating in exchanges. I personally choose Binance as the top exchange because they have very good policies for investors. Also Kucoin is only my fourth choice because there are still many other exchanges better than Kucoin