But even if the model is round and grey, leg length will vary, breast size and shape, neck length, all those other items of body shape will vary, so the round grey model can still give you no indication of what the garment would look like on you.
I am quite happy with a dress on a standard size model so that I can see all the features, of the garment. I then check that has the features that suit me or do not suit me.
Lets face it there are so many features to a garment that you cannot tell on a model, no matter what their shape; quality of fabric, thickness, quality of assemby, true colour etc.
As GSM says, essentially, if you do not know what clothes suit you/or not by the time you are 50, and if you cannot recognise these when you see them recognise them when you see them in a garment, you might as well give up.