CKing: I am afraid your understanding of what Hennig said and what cladists practice are incorrect. I recommend reading Hennig's book Phylogenetic Systematics, go to part III, then go to the subheading "Dichotomy and Radiation". There you will find Hennig writing the opposite of what you think cladists believe about the pattern of evolution. The dichotomous cladograms are only an operational way to visualize sister relationships and are in no way an assumption or constraint about how things must evolve. This has been explicated numerous times in the literature.

Have a nice Thanksgiving (if you are reading this in the US). Cheers to the rest.

BIC