I dunno … but Deobandis say Ya RasoolAllah (SAW) all the time … in the tashhud …
Assalamu’alaika AyyuhanNabiyu … this is harf nida and ism munada - according to rules of grammar - so if people are saying their aqeedah is wrong I wonder who they are actually saying salam to in their prayers?
Trust me there are ways to convince Deobandis - no need for takfir - just simple internal consistency checks will prove things.