What's the basis for this assertion? I do online banking, credit card payments, and the like and have been using Windows Security for years. As I said, and it's not just my opinion, Windows Security has consistently been scoring somewhere in the top 10 positions for the testing labs that evaluate security suites for years now. For all practical intents and purposes, these things are functionally equivalent on the whole.
Look at the most recent testing results from the following antivirus/security testing labs, along with the historical results from the past several years if you want to see how Windows Security/Defender has been performing. Windows Security has been solidly in the top 10, often top 5, and frequently beats out several well-known competitors that one must pay for.
AV Test (See Windows test section)
AV Comparatives (Reports Page – Look at Real-World Threat Protection and Advanced Threat Protection Test reports)
SE Labs (Reports Page – Look at Endpoint Security Reports)
MRG Effitas (360°
Assessment & Certification Reports)