You still usually need a TAN that's either on a piece of paper at home or generated by a special device (and with Smartphones, I don't really trust mTAN), with PayPal you only need a password. So yes, it's less secure, but more convenient.

Merchants also seem to prefer PayPal because it gives them an instant payment confirmation.

You're talking about Germany right?

Was never asked for this in Ireland, though they use an electronic token (because paper is outdated) if the transaction is outside of Ireland