That is not a good excuse for keeping McFadden over Morris. If Zeke is out, would rather have a good runner or a good blocker? I think it's stupid when you hear that as an excuse. This RB can block and catch but can't run worth a darn, but we're keeping him over the running back who can run the heck out of the ball but is not a great blocker. That make no sense.
I think it makes a lot of sense. Morris is the guy you want running the ball if Zeke goes down for an extended period of time. But he doesn't pass protect well, and you can't use him in the passing game, and he doesn't give you anything on STs. So any situation where Zeke is in the lineup, he's a liability in that he takes up a roster spot but can't be used. McFadden, on the other hand, is a change of pace for Zeke, and can be used on all three downs. He also gives you backup return potential on STs. The same goes for Smith, if he can demonstrate that he can give you what you need in a reserve capacity.
Besides that, a RB isn't actually running the ball most of the time he's on the field. Even in Dallas. You can't just discount what they do in the passing game. A blown RB pickup from Murray sidelined Romo a few years back. And we're pretty obviously putting an emphasis on using Elliott more in the running game this season. So, again, if he goes down, you lose that, which takes a lot out of your offense.
Weigh all that against the differential Morris gives you rushing the football over what McFadden gives you, multiplied by the likelihood that you'll even need him....there's not a good reason to keep Alfred Morris on the roster.
Which sucks, because he's a good running back and a great teammate. But it's true. So, you try to feature him with the #1 OL on the off chance somebody needs him later in the preseason as a potential starter--either for a team dealing with a suspension or something of their own, or a situation like in MIA where you might lose a RB for a period (though it looks like Ajayi will be back, after all). If you can flip him for a late conditional pick, that's a win.