if you use an iphone and download a wallet from the official app, how safe are you if you have clicked on links or even opened files from your iphone though? Or let say you preview a document on an iphone but do not open it. Possible your iphone is hacked/malware where you typing anything on phone would be a concern?
Thus imagine downloading a mobile wallet and it generating a seed. You write it down on paper. You send coins to it. But if you have any malware or keylogger on your iphone, couldn't that person see your seed that was on the screen? Then basically enter the seed on their own wallet?
Malware does not only apply to iPhone because malware is also available on devices that have internet because all this security only we can prevent in various ways, so mobile or desktop wallets are equally vulnerable to malware if we are careless in carrying out activities on the internet. So both mobile and desktop wallets are good and it all depends on the user which one is more comfortable to use and according to their needs.