Banking app vs website - security?

[LionessesRules]

I've been getting more and more frustrated with logging onto online banking (random customer number, digits from PIN and password, then a text to my mobile to transfer across Not helped by dyslexia).
DH suggested the app. So I've downloaded it. I can now get in with a 6 digt PIN. Does this make things much less secure? It's now on a phone that comes out and about with me, rather than a tablet that stayed at home. It needs less info to get into. And I've just set up a new payee with much less faff than previously. Why is one system getting more and more secure, and then a newer system seems to be much less complicated?

I always feel less secure on online banking for some reason. I have virus protection but always worry about unknown viruses so prefer mobile.
No idea which is more secure technically speaking.

You can usually transfer less money on the app. in one transaction. Maybe that's why.