My balance assumptions are made based on default settings (meaning class-exclusive recipes enabled) and an initial temperate spawn point (and no reason to seek out colder biomes. If you're willing to travel, you want to aim for equatorial or establish a winter base in that region).
You make some great points with the trading, having profitable trade goods positions tailor better and is an argument for the repeatable usefulness of the class abilities.
You've fully convinced me that tailor is better than I had initially thought.
That said, I'd still prefer it is reworked because while there are many strategies to make gears from traders, tailor is still a class that is bad early, peaks in mid-game, and falls off lategame as well. Cold weather gear is something you don't benefit from outside of a biome that experiences winter (and in temperate, only part of the year), and you only need it crafted once and then can repair it indefinitely. Tailored gambesons are excellent armor, and retain value as a "walk around base armor" but again aren't something that you need crafted repeatedly.
For multiplayer, a tailor could join in the midgame, craft all the cold weather and aesthetic gear that players would want, and then switch classes and most of their contribution would be made.
I believe that a class has flawed design if the benefits are largely external to the class itself, in a way specific to VS almost all tailor's benefits are recipe driven and gained from class-exclusive recipes being off, while their inherent downsides are significant and permanent. The class relies entirely on class-exclusive recipes to not be a strict downgrade from commoner.
Contrast with hunter or blackguard which have class-exclusive recipes but do not depend on them for their niche.
Honestly, I see tailor even in multiplayer as a flex class for an experienced player where they know it's weak in comparison but want to visually communicate via tailor only clothing that they are surviving with a weak class.