Realistically only the Light Sussex remains a utility breed in this country (although if you know better please let us all know)
Originally a dual purpose bird (that is one created to provide a good carcass for the table and some eggs but not as many as a light laying breed) it was a large breed : - here I will define that : large as in well framed and capable of putting on a good amount of meat over that frame;
Breeders working from the British Poultry Standards seem to be going for a very large framed bird but not concentrating on the meatiness. This seems to produce birds that mature quite slowly - with plenty of bone but not enough meat on for a good table bird.
The slow maturing means that although they may eventually make a reasonable meal it is not at teh growing stage when the balance of amount of meat and tenderness is best.
In some of the utilty lines there has been an increased egginess possibly because of their use in crosses with Rhode Island Red - to create a
sexed linked cross (this is the basis of the Calder Ranger for example). The hens could be considered smaller and in some the neck feathering has been rather compromised - rather a lot of brown flecking
The silver genetics in the Light Sussex has been used by some less scrupulous marans breeders in the past - they crosssed marans x Light Sussex and the progeny back to marans. This created birds who looked like marans but whose chicks were easier to sex at day old - the cockerels being much lighter
This meant that the productiion of the Marnas pullets was much more cost effective as marans tend to produce more cockerels thatn pullets and they are a big bird to rear.
However the resulting generations have been producing birds with white feathering; pale eggs; and fewer eggs than would be expected. This has given marans a bad name through no fault of their own.