SMS is like having someone shout your second factor off of a rooftop a few streets away, loud enough that you can hear it. There is 0 security on it and anyone with even a modicum of motivation can intercept it without you noticing (ever). This is bad advice.

Email is bad for similar reasons (although slightly less in terms of exposure if you use a good provider).

SMS interception is hardly a low bar for attackers. If you are being targeted by someone with these capabilities then there is a lot more you have to worry about. Many other 2FA mechanisms would be similarly vulnerable to an attacker with that amount of money and technology...

I thought bad guys could get your SMS only if they manage to clone your SIM or call provider to change the SIM by social engineering. In both cases service on my SIM will stop. Unless they are state sponsored, in which case they can just arm twist telecom provider to give them texts.

Could you please tell how they can sniff SMS without user ever noticing?