It is not suggested to keep or store your coins on any exchanges sir. They might shutdown their platform at any time and your coin is at risk. Its better to keep your coins or tokens on a wallet were you have the control for the private key.
Yes wallet offline has excellent security compared to most exchange. when we save the coin in exchange then we can not fully get the guarantee because the exchange is a third party service so everys moment we could lose the coin we have. Until now maybe only a few exchanges that have good quality that is like bittrex. But still only the offline wallet that can give us the best guarantee.
Offline wallet can guarantee your fund would be very safe but its not very usefull regarding to trade our capital.
Saving in offline wallet is not suitable for us as trader who want always trade at any convenient time so split our fund and use both platform would be more suggested.