Don't agree at all. There is nothing to support Frankie's betrayal until he thought that Mike tried to murder him (in fact, Frankie complied with Mike's instruction to meet with the Rosatos).
Frankly, I would never see Clemenza in that situation being garroted by the Rosato brothers. Clemenza would never agree to meet them like that in the first place. He was smarter than Frankie and must have had too much respect as he was one of the highest ranking members in the Corleone family for over 30 years. Frankie was seen as "small potatoes".
It's like the Gallo brothers trying to garrot Carlo Gambino. It would never happen. If it would have happened like that in Part II, the movie would probably have failed.
