Since betten does not mean tefila, then what was the problem the Lubavitcher Rebbe was trying to answer by saying his father-in-law was “Atzmuso uMahuso araingeshtelt in a guf?” (From the context this is clearly particular to him or Tzadikim generally not all Jews, so don’t say he was referring to the fact that every Jew has a chelek eloka mimaal.)
I was going to ask the same question to Chabadshluchah. I’ll add that in the footnote, the Rebbe addresses the strenuous objection to his admittedly innovative “hergesh”, and ignores the plain meaning of the Yerushalmi to bring a “source” to it.
He should have simply said they misunderstood him, it’s not a chiddush, it’s accepted in every circle to ask a tzaddik to daven for us, and sourced explicit Chazal saying this.