As a rule, a CTE will NEVER improve performance. A CTE is essentially a disposable view. There are no additional statistics stored, no indexes, etc. It functions as a shorthand for a subquery. In my opinion they can be EASILY overused (I see a lot of overuse in code in my job).
Check the cupcakes at the minimum baking time. If the recommended baking time is 18-22 minutes, check them at 17 or 18 minutes (just a quick peek, make sure not to let too much heat out of the oven). If the tops are rounded and no long appear wet, they may be done.
Frosted with sprinkles even. We had the batter mixed up and in the tins in no more than 10 minutes and the cupcakes took 18 minutes to bake. We removed them from the hot pan as soon as they came out of the oven (use paper muffin liners for this purpose). We then turned on a fan to cool them even faster.