Dunno dude, when you bring up "40 provinces of 2000-3000 regiments" as a big bonus for big countries I'm not sure what else you could be talking about. The idea that a minor country is even capable of carpet-sieging a nation like France or Ottomans (Really you're mad that Serbia can't carpet siege the Turks? ROFL) is absolutely ridiculous so I don't think he's complaining about that either. Everyone should be relieved that that can't happen anymore.
I can't be completely sure what he's thinking, but I've seen him carpet siege a 20+ province Muscovy with Golden Horde in order to destroy them quickly.
It might sound silly, but you need to do silly things to overcome silly things like lucky nations getting awesome generals at the start.
I don't think the price system is dumbing down; in almost 300 hours of playing EU4 I never once gave the supply and demand of trade goods a single thought. Unless you were doing a WC anything you could do to affect the price would have an almost unnoticable effect.
And during a WC you did not care at all.
For me, if the provinces would have been producing rockets or rabbits, the outcome would have been the same. I never, ever, planned around trade goods. I gave them a look at the start, noticed that they were completely irrelevant (except for gold) and completely ignored trade goods in ~800 hours of EU4, including 1 WC.
For them to be relevant they would somehow have to be tied in to buildings and other aspects such as these, and all these should be tied together in a dynamic and interactive system. Something that I could control a bit in intervals shorter than 50 years (the shortest time it takes to control a trade good, I'd reckon) and that would require my attention every few months.