..is a hotly debated subject. Like Harrold points out, easy to get mass in a 75 pound dog.
What is tricky is to get good mass in a dog under 60 pounds. Tricky, but not impossible by any means.
A bulldog has to have good mass, especially a dog (male). Mass without sloppiness is ideal (to me anyway).
There are many lighter weight dogs that do not carry any mass and they have trouble winning. This gets "blamed" on judges not understanding or caring about the standard.
Some people are more interested in the mass than the size.
It is good to prefer dogs on the bottom end of the scale, I certainly do, but don't forget they have to have some bulk to them.
Get proper size and mass then you've really got something.