Alternatively we could, I dunno, copy FFS2 and get rid of the stupid 20 dton Bridge requirement, because it makes no sense that a 200 dton ship needs the same size bridge as a 20 000 dton ship ?
If you do that, then the 200 dton Far Trader starts to become viable against the 20kdton Far Trader - "but it's a niche" doesnt work in a low-trade universe, because for anything other than small urgent packages, you're generally better off waiting the 10 weeks for the scheduled big freighter to come through, and for small urgent packages you have the Type S.
The quantity of trade in the Traveller universe was never quantified until Gurps Traveller:Far Trader ... but the fact some worlds are specifically listed as 'Non-Agricultural' should be a hint that at least some worlds move kilos of interstellar trade per person per week.
That this level of trade is possible is easily seen from the GWP numbers in Trillion Credit Squadron or Striker, both of which are CT products - lets assume a person consumes a dton of food a decade (10 tons, one ton per year, 3 kilos a day). Assume food costs Cr 5000 a dton at an Ag world, or at least an a non- NA one.
One Far Trader doing three jump 2s with a week turnaround each end (ie load+fuel, jump fuel jump fuel jump unload ... no stuffing around for a week in each transit port) - thats call it KCr 5 for the freight, so KCr10 total. As thats 10 years worth of food, thats a Cr1000 per year, and easily viable at any sort of TL.
That Far Trader with call it 100 dtons of cargo capacity takes 5 weeks there and 5 back per run, 5 runs a year, therefore supports roughly 5000 people.
Is it going to be cheaper to buy and maintain algae vats and so on for those 5k people, or obtain one Far Trader to go three jump-2s to a world with a decent biosphere,to which we can also export whatever the heck our planet makes as a backload while moving the food in ?
This is the logic that makes the Third Imperium a high-trade place - it's got a lot of crappy biospheres, a lot of different tech worlds, and a central government that has the preservation of trade and the suppression of piracy as a founding principle.
And with a lot of trade, then you get your little niches.