Taylor pays McDonald’s (guessing) for exclusivity rights so they can sell a bad product

This is conspiracy level conjecture. The machines are fine when they are maintained and operated properly. The primary issue is that they aren't maintained properly.

But what isn't is McDonald's focus on consistent product between all locations - a milkshake you got at a store in FL must be the same as you get when you go to ME, IL, WA, or AZ - and even international markets. This is the clash of two different corporate priorities. The Taylor exclusivity thing comes down to the unwillingness of McD to spend man/hours training staff to have other machines as well as have interchangeability between stores (as franchises and even corporate buy/sell locations fairly regularly.)

For other equipment, the result is the same (fryers product the same product as long as they are the right temp, same oil (that is regulated as well), and same cook cycle. Same with the platen grills - the options allow for better scaling for restaurant traffic needs (some restaurants only need 2 sets of grills, others may have as many as 6 sets etc.) As long as they are set up correctly, they don't have the same consistency of product issue as the ice cream machines. This even goes into the standardization of product - a hamburger always gets the same single dispensing of ketchup and mustard, slivered onions, and two pickles, etc. The amounts are calibrated (except for the onions) for all the standard sauces - ketchup, mustard, mayo, tartar sauce, mac sauce...