It may be a “only” a shtus, but it’s a dangerous and harmful one.
Still, the OP’s tayna doesn’t work – the false moshiach is still alive, so why would he need Moshiach min hameisim as a defense? Hrs not taynaing anything after he died.
I personally find Redleg’s tayna more compelling than the OP’s. Still more compelling is the fact that until the Rebbe’s petirah, the idea of Moshiach coming from the dead was never accepted as a mainstram position in Klal Yisroel, even in Chabad/Lubavitch. That’s why his petirah was so devastating to those who believed he was definitely Moshiach – because it totally didn’t fit the narrative. Some of those who couldn’t wrap their heads around the fact the Rebbe wasn’t Moshiach retrofit their hashkafa around his petirah, finding sources which may or may not support the notion – but at most those sources had the status of a daas yochid (bracing for comments about my screen name).