To compare a Excellence to an Open Pro or a Nemesis to a Reflex is an unfair comparison.
I'm obviously comparing the Open Pro with Ambrosio's clincher equivalents
and the Reflex with the F20's.
Keep in mind that the braking track of Mavic is much better than Ambrosio. Ambrosio side wall is not machined and will likely pulse under breaking at the joint. And that the reflex is a tad stiffer than the Chrono.
I ride Ambrosio Crono F20 and GL330 & SSC from Mavic. All are beautiful to ride. By contrast the Reflex rims I have felt dead. The SSC & GL330 rims are laced identically to the Reflexes. Nuf said
I value your personal opinion (I really do), but that in itself is not enough to claim that Ambrosio is head and shoulder above Mavic especially if there are reports going exactly the other way around.
Here is our forum colleague Coloclimber:
I have had both laced to Record hubs and like the machines sidewall, width and strength of the Reflex better. The Crono F20s were a bit too light and flimsy for my weight. The Reflex are great rims.
The claim that Ambrosio wipes the floor with Mavic isn't based on much beyond your personal experience it seems.