OTPs are great, until someone calls up your phone company and social engineers their underpaid support staff into giving them control of your phone number.

This is not speculative. I've literally had to help relatives with this exact security breach.

Using phone numbers for 2FA is insecure for that very reason. You are entrusting all your personal security with the phone company. Using a OTP by phone number as your only authentication factor is much less secure than a password + 2FA.

An authenticator app, such as Authy, faces none of those security issues.