There are several flaws in your logic, but the biggest one is this - Mudiay is not Magic, he won't be MVP this coming year. And if we're not making playoffs this year, DMC is as good as gone (and nobody can blame him). Which means no, you won't be pairing the MVP Mudiay with DMC any time soon.
Bottom line is, this coming year is as close to "all or nothing" as it gets. We cannot spend any time grooming potential, no matter how high the ceiling is. We need as close to a "sure thing" as possible, and WCS fit our needs like a glove.
Neither of them is going to be a huge help in this playoff run- they are rookies... and you can't count on rookie's if you want to win.
I like WCS because of his ceiling, I think there is a good chance he can become a very good defender and if he develops properly he has the chance to become a better cutter and score effectively like DJ or Brandan Wright, he also showed that he can develop a workable jumper.
But I'm not expecting him to do any of those things this year, atleast not the first half of the year. I'm not even expecting him to be a good defender, rookie's struggle- check out the players named "NBA ready" and see how many of them was actually able to bring anything to the table their first year... I'll quote an older post I made about this:
If we look at last year 2nd season players you could see that adjusting is usually needed:
1. Ben's DFG% (defended field goal precentage- the field goal precntage of the opponent when the player is defending the shot) is equal to the usual FG% of that same player on average this year.
While as a rookie players shot 4.5% better on him than on average, which is a HUGE difference as a defender.
2. Otto Porter DFG% is 3.4% lower than the average FG%- meaning he was a good defender this year.
While as a rookie players shot only 0.5 precent worse on him, again a huge difference in defense from first to second year.
3. Anthony Davis was supposed to be a defensive monster from the moment he reached the league, his rookie year he made players shot 2.7% worse on him- which is pretty good, but in his second year he became MUCH better- making opponents shot 6.2% worse than usual.
Of course that the FG% of your opponent isn't the only part of defense but it does goes to show that between year one and year two players can improve a lot defensively.
Could WCS be a solid/plus defender his rookie year? maybe, but I doubt he will be good enough on defense for you to want to start him despite his offense.