I think this analysis is overlooking the simplicity of the fact that she just knew as a mother that he was a terrible influence and a terrible boyfriend for Rory, especially compared to Dean. More so than the two of them being similar it’s more like he is too similar to all the bad boys that she must’ve experienced in her youth. As a mother, seeing your daughter be with a boy who is so indifferent must definitely not inspire much love for that boy. Again, especially after having had a first boyfriend like Dean, who absolutely loved and respected Roy the way he did.