I disagree, I think the KitchenAid mixer (at least the metal gear Pro line / lift bowl line) are just FINE for heavy bread doughs, that's what I use mine for. The PROBLEM with their mixers is in the assembly (they don't loctite their assembly screws so the screws back out and the gears jump in the transmission, causing stripping and motor over-loading) and the lubricant they use.
Loctiting the screws so they NEVER back out and using a grease that doesn't turn into a solid in 5 years is the absolute KEY to KitchenAid mixer longevity.
I have two KitchenAid mixers a 6 quart pro that I’ve had for a couple of years. I rarely use it.
The other is my primary mixer. It’s a 20-year-old tilt head KitchenAid mixer that has seemed more mixing than you can ever imagine. Still going strong—in fact never even had the grease repacked in it and has never stripped a gear. I’m thinking though it is long overdue for some grease.
if your theory was correct, my tilt head would have blowed out 15 yrs ago. Then again 10 yrs ago. And it should have blown out again this year. I‘be passed the five year mark three times already on that machine.
I’m very careful never to mix heavy doughs with my KitchenAids. As a baker of 20 years and one who’s had a lot of professional training I know that the appropriate mixer for heavy doughs is a spiral. If you go into a bread bakery, that’s what you will see. And if you get Jeffrey Hamelman‘s book Bread, all use of a mixer will refer to a spiral mixer, not a planetary mixer.
Aside from not handling heavy doughs, planetary mixers do a terrible job kneading dough. They create a tremendous amount of friction because wrap around the dough hook and just just drag the dough around the inside of the bowl. The heat is bad for the yeast.
The drawback with a spiral mixer is a good one is expensive. And some like the Famag Grilletta are designed just for doughs.
If you watch the video below you see there’s a significant difference in how the dough moves in the bowl of a spiral mixer compared to a planetary mixer.
Both the mixer head and the bowl rotate; you can see in the initial stages of mixing the water gets worked through the dough much more thoroughly. The dough does not get wrapped around the dough hook and dragged around the bowl. It also doesn’t get stuck to the bottom of the bowl and endlessly twisted around.
this is the spiral mixer at the training center where I take a lot of classes.