Yes, we have a historical science. But that does not mean that we do not develop testable hypotheses. We develop testable hypotheses of homology between character states, and test those hypothe ses for congruence against alternative trees. I think there is more to it than that.
Simplicity is inherint in the scientific approach.
I disagree, That is not the justification for simplicity per se in systematics. It may be, in a sense, a justification for doing systematics in general, but only to the extent that if convergence was ubi quitous, then one would have no hope of ever discovering historical relationships. That gives liscense to our science in general. Simplicity tags along, since it i s an inherint part of science. Mostly, but not all.