Why? Too much? Too little?

The egg seems to be the most reliable scale indicator? Assuming that's a normal size egg, that is a very large plate of food.

I know the intent is to indicate relative proportions of food, but you question suggests more work needs to be done on portion control also.

I think if you divide the food on the plate over the course of a day that might be a reasonable amount, maybe a bit too much. Generally the site tends to focus too much on the problems of overeating while some people (myself included) might rather have problems to eat enough (healthy) food sometimes.