Wow, that's a bad idea that you do.
Don't save your Bitcoin for a long time in the Exchange wallet.
Because the Exchange is very vulnerable in its security hack by hackers.
Be careful friends.
I have some coins on exchanges and feel pretty safe, but I am only using Binance and Cobinhood and these are exchanges that have more than 90% in cold storage. From Cobinhood I know they have even 97% in cold storage.
So I don't think it's black and white...it depends which exchanges you use, how often you are trading and what the alternatives are. Most people I know don't have a Nano Ledger at home, just have their token on MyEtherWallet...and this one has been hacked several times. At least it is easier to hack then secure exchanges Binance or Cobinhood.