This is not always true. It is like saying someone who has funds stored in different centralized exchange has a safer setup than someone who has just a single hardware wallet. There is nothing wrong in using multiple wallets, but the security of your funds does not depend on the number of wallets you use, but how secure it is. By secure i mean, is it offline, how well have you stored your backup, did you add an extra layer of security, i.e. a passphrase, etc.

My point here is that some newbies may think they are safe just because they use multiple wallets, which isn't true, except the wallets are secured in the right way and the user knows exactly what they are doing.