I disagree, yes that is the idea behind introducing consumer goods but that doesn't mean they can't or shouldn't expand it. And making it so trade alleviates some of the costs of consumer goods would be a great way IMO to offer a clear benefit to allowing other empires to exist and to buff the peaceful/international play-style.
I'm not saying it's a bad idea, I'm just trying to point out how much you have to do before you get to the OP's stated intent. The whole idea of making small empires more potent at trading still suffers from the same fundamental issue that affects all "tall vs wide" discussion in Stellaris.
Let me take your ball and roll with it: assume that in 1.6 or something, they introduce Factories, which are built in Mineral patches and produce Consumer Goods as a separate resource -- thus creating a market of efficiencies, since Consumer Goods are effectively produced from Minerals, but different Empires will have different tech levels, thus creating different efficiency levels for the Mineral:Consumer Good production. Thus Empires with good M:CG conversion would be able to trade to Empires with poor M:CG conversion.
That would be a good start to hashing out a more evolved trade system, but what it would not necessarily do is make larger Empires more reliant on smaller Empires for trade -- a stated objective of the OP. In fact, this could well be
counter-productive: if the larger Empire has the tech edge*, it might well be more efficient than its smaller neighbours -- thus being able to sell them CGs for Ms, and getting a profit out of the bargain.
* (I know smaller Empires are more efficient at research tech
in theory -- but I'm sceptical at how that holds out in practice with human players, who will create dedicated research planets in their large Empires and thus likely out-tech their opponents.)
EDIT NOTE:
Possibly one way to introduce better efficiencies for smaller Empires would be to introduce civilian/local trade modifiers.