The bigger building size does not matter much.
They may be bigger, but therefore they also produce more, when you calculate it down to one square its close to even: Silk: 28.5 per square, marble 28,8 per square, gems 28,6 per square (Level 15 manus without boost)
And that's exactly my point: To produce 1k tier 1 one goods you need the same precious space and time, as producing 1k tier 2 or 3 goods.
The trader ratings (and the wholesaler) doesn't consider that, only that you need 4 times / 16 times more coins and supplies to produce higher tier goods.
Time and space is very valuable for me too, so for me the rating is not fair and I think for other people too: Seeing much 3 star offers of tier 2/3 goods demanding lower tier goods sitting in the trader for days. The other way round I barely see lower tier goods offered for higher tier goods and if I see 'em I most of the time take them even if they are just 1 star
With all the repeatable quests it's hard to run out of coins/supplies so the higher production costs don't matter much, but the time and space always does, at leat for me.