Says who? I have only heard anecdotal evidence that some people feel their car under steers more with the front brace installed. If the front brace is reducing flex that much that it affects handling then I would say it's doing a great job of bracing the strut towers. If under steer is an issue with one I think that is a good indicator that there are other issues to be solved with suspension geometry. A chassis can never be " too" stiff...