the original question was about Aikido vs. Kenpo or Kempo ?
as for other reply about on aikido vs. kendo stances, be careful about generalizing about aikido stances. Kendo is a lot more uniform about what is correct kamae. I wouldn't say kendo stances are unstable at all. Stability has more to do with you internal state of relaxation and how well you physically understand you own center of gravity. All that affects you ability to move in different directions with speed.
There is quite a bit of variability between aikido schools on what is correct stances. Any stance on two legs is inherently unstable in some direction. It's really a miracle that we are so stable on two legs, just asks the robotics engineers. A lot of things go in to your balance you may not even be aware of (try being stable without your big toes). If you tend not to have your back straight (I would say to students, keeping your shoulders resting over your hips), that would be viewed as a mistake in our school.
Well, one of the biggest differences between Aikido and kendo is that in kendo they tend to have a rather unstable kamae compared to aikido, because they have no need in moving sideways in kendo when they have this big protective armour thing called "bogu".
In Aikido we always lower our hips and stand in a stable hanmi because we have to move in different directions. In aikido we don't use (or have the access) to an protective armor which prevents us from full-contact training like in kendo. Another thing that differs from kendo is that we tend to not have our backs straight. (I don't really see the point in doing that, but it's just a thing we do).