Lots of convergence, too. The above scenario is reminiscent of an incremental, functional theory advanced by another George, George Gaylord Simpson. Ironically, unlike BCF Simpson's horse phylogeny was incompatible with fossil stratigraphy.
Plausibility is a useful yardstick, but it depends on the eye of the beholder.
A reading of the literature would suggest that not all find non-arboreal hypotheses implausible. The critical question is one of methodology. BCF adherents prefer an incremental, functionally plausible narrative, while adherents of phylogenetic systematics prefer a repeatable, testable methodology based on character distribution. The latter requires that functional narratives conform to, rather than dictate, tree topology.