1. It should just be plain unnecessary to apply such a hack.

2. There is still a single weak point for all services.

3. While this prevents against the run-of-the-mill "attacker activates another SIM card for my mobile number and steals my crypto cash from $online_wallet" coming up here every few month, a more sophisticated attacker can just route the SMS to himself via SS7 (I suppose the SIM variant is easier to pull off with less traces, and obviously requires much less technical expertise).