A plek machine will give results that are commensurate with the person setting it up. It isn't magic. There is still a human in the loop.
Yes there is a human in the loop but that is for optimizing.
When it comes to a really bad setup a Plek machine simply can't give it to you. And yet I can say I have had a bad setup from a Plek job!
Once I explain it to you, you will understand. I took my Conklin 7 to the local Plek machine. A local luthier had just bought the machine and was rather a noob on it. Hence there was a lot of cellphone traffic to the PlekMeister in Nashville. Basically the noob was talked through all problems.
Now understand this. The Plek machine has built in all manner of "protections" to keep the human operator (or a weird instrument) from causing a really bad job. Anytime the Plek computer senses that something is about to be done that it considers "wrong" it simply stops and demands from the human if he REALLY want's to do this! Hence to get a nasty setup out of a Plek machine would take a LOT of human overrides!
So How did I get a "bad" setup? Well, a 7 string bass is right at the limit of what the Plek machine can do and it took a lot of coaxing to get it to finish. Except it didn't finish! It got down to the last two frets and quit. Apparently it decided it couldn't go that far up a 7 string neck. Anyway, panic call to nashville guru and he says: (get this!) "Bass players never use those notes that high up the neck anyway!" So the Luthier (and he's a good one) did a quick finish on the last too frets by hand. But he was in a hurry and worn out from Pleking and later I find those two frets are really still too high. Well, I've got a fret file so it's no biggie. but you can see why the Plek machine won't let you have a bad setup UNLESS it stops and complains and you don't bother to finish the job.
So anyway, the Plek owner was pretty much as newbie as they come and it still made all but the last two frets play like butter! So if someone says the Plek did a bad job, you know it's either not true or the human had to do a lot of overrides to make it finish what it didn't want to do.
I really doubt that a production Plek machine on the factory floor would have a newbie running it...but things happen.