Yes, Maine Coons can be normal-sized. It is a good question because there is a slight obsession about Maine Coons being big and breeders tend to follow this and make them big, sometimes huge. Maine Coons are known to be big and the biggest domestic cat breed. The fact is though that the CFA breed standard for this cat does not specify that they have to be big. There is nothing making it obligatory other than customer demand.
The general introduction in the CFA breed standard states that cats of this breed should be solid and rugged. And ‘quality should not be sacrificed for size’; a hint that they prefer smaller Maine Coons which fit the breed standard over monsters that don’t.
TICA breed standard is slightly different in that they demand that the cat be ‘large, long and substantial’. The word ‘substantial’ means large in cat fancy language. But weights are not specified and ‘large’ is an elastic concept. Size is relative and therefore even TICA are not insistent on huge Maine Coons.
Google search throws up a weight range for females of 3.6 kg to 5.4 kg. At the lower end this is about 8 pounds which is the average weight of a domestic cat. Can Maine Coons be small? Yes, females at the lower end of the weight range can be an average weight which is not small compared to all other domestic cats but relatively small to other large domestic cats including some Maine Coons. And in the USA the average weight of domestic cats is probably nearer 10+ pounds so 8 pounds is relatively small. Although I doubt that you’ll see many female Maine Coons this small.
The shaggy medium-longhaired coat tends to cover up quite a lanky body. These are not chonky cats. They are quite slender which is why they are described as long. Remember Stewie, and Aussie Maine Coon who was decribed as the world’s longest domestic cat? A stupid title but the point about body conformation of this breed was made.
There is another point. The experts say that the Maine Coon (MC) is a slow-growing cat not reaching adulthood size until they are four years old. This means that they’re going to be smaller than usual for the first four years. This is about 25% of their life!
Breeders take differing veiwpoints of breeding for size. The Russian MC breeders sometimes go mad and create monsters through careful selective breeding while other breeders in say the UK don’t focus on this aspect and breed relatively normal cats.
And there will be a natural variation in size in offspring. You will have some small MCs which answers the question in the title. We don’t hear about them because all the focus is on the monsters and I admit I do that as well.
The creation of very large MCs is a natural consequence of human nature: to always seek ‘improvements’ which in the world of this cat breed making them bigger.