yes well GLA and CLA both compete at the same price point, but they serve different needs and wants.
most makers stagger their pricing so that models do in fact overlap, its a form of upselling. Imagine you can get yourself into a Q30 for ~$40K loaded, yet you can also get yourself into a scarcely optioned QX50 at that price. For a few thousand more you can have everything you want in the larger car. As the models get more expensive the maker makes a bigger margin. When you average out the payments in a lease or finance scenario the increase of a few thousand from Q30 to QX50 works out to peanuts per month.
Again its all about needs and wants. Just because you can get yourself into a QX50 at the price point you want doesnt mean it will serve your needs.
Same with Q30, at its expected $30k MSRP you could also get yourself into a 370Z, but does the 370 meet your needs?