To be fair, for OS we didn't have Destroy All Aliens at the time, and it wasn't confirmed as a What If episode til later on when we had sequel series. This was originally to set up a whole new chapter for Ben 10 since MOA was currently planning the next series before they were replaced by the people who made Justice League.
Race Against Time also wasn't canon because well.... that was obvious.
I think this was just to give OS a proper finale before going into whatever might be the next series because you wouldn't wanna end it on some plot heavy two parter without a set up or proper finale. Honestly it was nice.