Email 2FA:

While Email 2FA isn't as secure as with an app. It is easier to setup, and still provides a extra layer of security. Many game services offer this as an option including: Epic Games, Origin, and Steam. It would also provide an option for those without a phone who still want extra security. 

What would be more secure...

X% (you should have the numbers) of people signed up for the "App 2FA" or 100% of people signed up for "Email 2FA".

Sincerely, -Arcosh