this is a wrong interpretation based on the Quranic Ayat being quotes , As a Muslim we believe that all prophets are equals and followed Allah orders and command but when it comes to following we got this text from Prophet Muhammad PBUH and the declaration of shahadah specifically state that we follow what is reveled to Muhammad and not any other prophet

On the second point of saying PBUH , it is out of respect to the prophet like we say greeting on Peace when we meet. God does not need to show respect to the Prophets ( they are his creation) so using that as an analogy and making it as a hard rule for publication is not right in my opinion

As a Muslim we should we welcoming and should not have a small concrete mindset; please consider referring to scholars or learned ones when making these rules