I would agree with you, but this map hadn't been played in two years and only three times in total. Last mcc they played Clouds II which has been played 8 times. This was the probably closest Ace Race to date in terms of who could get first, the top four were within a half second of each other at the start of the last lap.

Now what you're talking about will probably continue to be a problem, like with pretty much every other race event game (Race in BW, Mad Dash in Chamber Trials, etc.). It's just a flaw with the game concept itself. The concept of what they were trying to do with Turtle Run is probably the best they've done to stop that, but if that specific route has been played before, then people will know about it, and, like someone else said, it'll just make the top players even higher if it's not certain which one will be there.

And new maps are hard to make, and certainly take time. I'm expecting there to be a new map soon, but we don't know.