rolling mass vs diameter which is the greater evil

This is a 195 80 16 sat on 16x7 grand vitara rim
Has you can see the tyre sitting almost in line.... No side wall bulge /balloon 


This is a 205 80 16 on same rim
 
Never got to use the 205 80 16 even with a 4" lift the outer tread lugs rubbed terribly

This now
 

Probably worth noting. Those Insa Turbo remoulds are abnormally large for their rated size. That 195 must be as wide as a 235 easily. A “proper” 205/80R16 is incredibly narrow. 

Here is the Freelander with some 205/80R16’s. 
 

When I used 195 80 16 my spare at the time was 205 80 16 marshal mt not really aggressive tread and dimensions wise where all most identical 

All tyres have a range of wheel widths that the manufacturer deems appropriate for it to be mounted on. For high profile tyres like you are looking at the wheel is usually a fair bit narrower than the tread widths of the tyre so as an example a 205,80r16 is nominally 8 inches wide at it's fattest point which isn't necessarily the face of the tread, and such a tyre would expect to mount on a wheel somewhere in the range of 5.5 to 6.5 inches wide. This is a function of the construction of the tyre. To then mount it to a 7 inch wide wheel alters the way it sits on the wheel which can shorten it's service life, cause it to over heat, and run the potential for it to unseat the bead from the rim. Now obviously a difference in width of half an inch isn't that bad in reality but it is something to be conscious of.