I suspect your argument is theoretical, and not based on experience. I play on different worlds, and have cities with different boosts. Here's what I see.
My scrolls-boosted cities don't have much of a problem. I simply don't build very many scroll manufactories. Instead focus on my T1 and T3 boosts and then post cross-tier trades to get crystal and silk. I stockpile and then it's not really a problem for me. Occasionally, I have to do some trades to adjust. Plus, I chose to join fellowships where at least one of my boosts was in demand. So it's not much of an issue for my scroll-boosted cities, although it's not to say it doesn't mess up plenty of other people.
Sentient goods are much more of an issue because you can easily get screwed over on all three tiers. I have one city whose boosts are moonstone, obsidian, and Cosmic. Every one of those is in low demand, with cosmic being the worst, followed by Moonstone. Because sentient goods are constantly required for advancement AND because I can't stockpile, I'm constantly having to waste time posting 3 star trades and then wait, hoping someone will pick them up. On another world, my boosts are Platinum, Ink, and Soap. Every one of those goods is in demand. So when I need stuff, I just go to the trader and there's the stuff I need, often in the form of a 3-star trade. The play experience is totally different, with one being constantly annoying and the other pleasant.
I quit a city I worked on for about a year because I could not trade away my scrolls. I was contantly openeing my hand pleading with others to help me out, and since I grew fast my hand was becomming bigger and bigger.
It's not just theoretical.
if... and I say if.... you can get away with scrolls as boosted goods, then feel yourself lucky.
And yes each world has it's prevalent goods, and some that are in a oversupply.
I also assume you are talking about established worlds. try playing scrolls on a young world where there is no legacy. you'll be playing a nightmare. because these worlds cannot absorb these inbalances like a old world can. but at a certain point also old worlds will succumb to this issue. it's not a matter of if, but when.
No one tells you to set 3* trades, that treegum decays just as well as moonstone does.
Just post trades and have patience. this is something that's in short of supply at many players.
Thanks to the spire there is outside other parts of the game a constant need of everything.
Moonstone, tree gum? it's seldom for sale in the market where I play, so I post trades and wait, most times it takes pretty fast seldom it takes a bit longer. to many people seem to be afraid that someone else might get "my" trade and do crazy stuff.
On the world I play obsidian is the T5 in demand. and bismut is the only one that is in a real oversupply.
but you know what, no one has a stockpile of 15-20m bismut, and because of that people like myself are in a constant need for bismut.
I also take 2 star trades above 3 star trades. just because I prefer to deal with people who are less impatient. so outside my fellowship I ignore 3* bismut trades as much as possible. not seldom I just clean out the entire market.
I have read an interesting theory, with at least on the new worlds, many scroll players are quitting the game (like I did). as a result in the future this might result in a massive shortage of velvet production. if you make it to that point your scroll boost might turn into a blessing in disguise.