Of course user behavior has to be considered. The MePIN app does allow the user to set up a personal PIN code, so an authorization would then require the PIN code and a tap.
I think anyone who would blindly use your proprietary two factor solution that makes it easier for end users to authorize other people to log in would be silly.
'No 2FA' is the real silly one here. Any 2FA is so much better than no 2FA, and usability has been a big issue so far in 2FA adoption.