It should be the whole dog, conformation and movement.....movement means how the dogs are evenly based to the ground, holding topline, good reach of neck, correct stride etc etc... not how the dog roll from side to side and literally pound the ground....
as for a massive difference in weight...Tia is a good old fashioned
very tall bitch (bordeline top heightwise, but gets away with it (sometimes)

She weighs a whopping 38kg....BUT she works like a little trojan and ALL her weight is solid muscle....when she moves her muscle possitively ripple with taughtness.... Ellie on the otherhand, was a more delicate midheight range bitch and at only 14months when she died, had not reached her potential, (I prefer my dogs to come on slowly and reach maturity around 2 maybe even 3years....Ellie was getting there and at her penultimate show, she beat Tia into 3rd place, she was just over 10kg lighter, , but I moved her better than Tia moved (Tia had a handler that had not worked with her before) ..........Sooo many Labrador puppies now are coming out into the ring for the 1st time looking all the world like fully mature adults....
At a show today, I took my pups (4.5months) along for a couple of unbiased assessments....and was told to watch their height, too tall,,,,and get some weight on them....ahem, they have already reached 20kg+....my weight comes with well formed muscle.....not fat :) OK they may not be the 'perfect Lab' for todays showring, but they come very close to their ancestors of 40 years ago ;) and thats how I like them, and I will persist in the showring....Oh and yes, they will work too :D