By what measure did you determine that? Do you have the ability to determine that there has been no deformation to an installed part? (Some deformation occurs every time an interference-fit part is installed.)

Could you provide a picture of the generic press being used in such a way that is applies pressure to the ball joint flange? Every example that I have seen shows the press applying pressure to top of the housing in a way that is guaranteed to deform the part. The deformation may not be easily detected by the average shade tree mechanic, but it occurs nonetheless.

I have personally seen one ball joint that was completely loose (meaning that the ball flopped around in the socket) following installation with a generic press. That may have been an extreme case, but there is no doubt that some deformation occurs in any case.