Create an empty ship, then retofit it to full ship for only 50% dust, is it normal?

An empty minimal corvette costs 44 industry or 80 dust, plus retrofitting to the full 120-industry model costs 60 dust. Total (44+60 ID) or (140 D) versus (120 I) or (278 D) by standart building. Is it a good-balanced feature?

Investing dust by this way, gives the converting profit about 1 : 1,25 (dust : industry), instead of standart 2-3 : 1 at the dust-boosting production (I don't know by which formula it's calculated).