Hello, I have simple yet effective idea that would allow merchants to be viable again (as long as markets wont be connected, like in the old days).
Make few important resources region specific, each city would have their own resources in the area (I mean common stuff like fiber, iron, wood, stone).
Small amounts can be avalible everywhere for personal use, but definetly not to farm/power level professions.
This way people who like farming resources for money can supply closest city, and people who want to be merchants could distribute it all over the map for profit.
Im assuming that this was the original intent of the devs, but making resources widely avalible made some cities almost dead while 2 others took all the profits. Connecting markets did not change much as peple still have no reason to reach other cities to sell their stuff.
If you dont want to make storage city specific again, just add a city tax for moving large quantities of one resource in short period of time, like 6h cooldown per stack/some weight.
Tell me what you think, or what would you change to make it work even bettter