In cases where change is step by step over long periods of time , common descent makes a fairly narrow range of predictions.
However, the faster the change, the bigger the leaps involves in each step… the set of possible outcomes become bigger. If you have a big enough toolkit, all things are possible… hence common descent will predict every alternative.
This is one of the disadvantages of not being coupled with a specific mechanism.
Edit: Add to the above, the conviction that there has to be some natural explanation for all phenomenon.