Yeah, labs generally do have to gain weight to go from conformation to other competition. Our handler had labs and they'd have to put on weight to even get considered. It's like that in a lot of breeds. I can't figure out why- dogs don't look good fat.
And even field bred labs shouldn't have a huge tuck up. It's just their build, they're supposed to be stocky. Our field dog was a rather stocky guy himself (though quite a bit leggier than many show dogs I see nowadays) They are however also supposed to be athletic and not fat like you see in many shows (I've seen some awful conditioning on labs at shows).
And even field bred labs shouldn't have a huge tuck up. It's just their build, they're supposed to be stocky. Our field dog was a rather stocky guy himself (though quite a bit leggier than many show dogs I see nowadays) They are however also supposed to be athletic and not fat like you see in many shows (I've seen some awful conditioning on labs at shows).