This is a oxymoron because Power is one end of the Strength spectrum with Endurance being on the other end.
why are high-rep O-lifts...generally frowned upon,
1) Skilled and Technical "Movements"
Olympic Movement require more skilled and are a more technical movement that a Kettlebell Swing.
While there some skill is required with Kettlebell Swings, it is a much easier and faster to learn.
2) Power Movement
Olympic Movements are a Power Movement. Research has demonstrated that Olympic Movements produce some of the greatest Power Outputs, if not the greatest.
That is one of the reason that Olympic Movements are part of most sports training programs.
There is an indirect relationship when it comes to the number of repetitions performed in a movement and the development of Technique and Power.
As the number or repetitions increase Technique and Power Output goes down, deteriorates.
With high repetition Olympic Movement you learn to perform the movement incorrectly. You increase your Endurance at the expense of Power.
One of the reason that CrossFit is criticized in this case is that they take a Power Movements like an Olympic Movement and use them for something other than their intended purpose; using them for Metabolic Conditioning.
To reiterate, high repetitions Olympic Movements definitely blow your heart rate through the roof. However, it come at the expense of developing poor technique. Strength Endurance is developed at the expense of Power Development.
The Wrong Tool For The Job
Does the technical difficulty of the O-lifts just make them impractical for power endurance?
1) Power Endurance is a oxymoron.
2) Performing high repetition Olympic Movement amount to using a Crescent Wrench to drive a nail rather than a Hammer. It works but it not the right tool for the job. Constantly destroys the Crescent Wrench; it not going work for it's intended purpose.
Yes, they are the wrong tool for the job.
The Kettlebell Swing Paradox
Is it because kettlebells are much lighter and so fall into the power endurance range?
The Kettlebell Swing is an exercise paradox.
1) Metabolic Condition
It is an effective exercise that can be used for Metabolic Conditioning with light to moderates loads with moderate to high repetitions.
With that said, the movement should be stopped once technique falls apart.
2) Power Training
It can be used to increase Power Output when with heavy swings (30% push of your body weight) for lower repetitions.
Paradox High Intensity Interval Training Example
A paradox amount to a contradiction from the rules.
Research shows that High Intensity Training is a paradox. It increases both anaerobic and aerobic capacity at the same time.
"The high-intensity intermittent protocol improved V02max by about 14%;
anaerobic capacity increased by a whopping 28%." Source: Forget the Fat-Burn Zone