I merch too, and I do admit, really anyone can just start doing it and turn a profit extremely quickly (there are many resources out there, prominently Realmeye, that make the whole thing 100x easier). It’s easy to do, and generally reliable, and UT’s wouldn’t be an exception to this, because as you say, they too would have their value drop simply because of those people selling them off.
That’s why I suggested a limit on UT’s sold and bought. Sure, you CAN still buy a Jugg, provided you had the right items. Let’s say it cost 8 Pyramids (just using these numbers as placeholders). There would be no cap on how many Pyramids you can get “normally”, and so if you farmed enough Tombs, well you’ve got yourself a Jugg, which I think is somewhat fair (see my Abysses to Ogmur argument). I think what many fear is someone who just sits around buying and selling, and merching up to that Jugg.
Naturally, if UT’s were no longer SB, the only thing worth enough to buy them (at first) would be other high value UT’s. And so, this person who just merches all day could buy enough Pyramids and get that Jugg. With a UT trading cap (which includes any UT’s bought or sold), you wouldn’t be able to get to that point, and I think this problem would solve itself.
As for your second point, I don’t really know the impacts of RWT personally, and I don’t know if it’s as evident as duping, for example. A good amount of people would be willing to sell off a Jugg for like 10 bucks, because even though that Jugg was rare, that 10$ is actual real live money, despite this not being allowed. I think the case with Decades is majorly because of duping, although yes, RWT did play a big hand in them being so damn cheap. The fact that the price of them have basically remained stagnant proves that they can just keep being multiplied, no matter how many are sold and lost due to deaths. So, even though some people may buy a bunch of them for hella $$$, the amount of Juggs in the world doesn’t go up. The price would remain stagnant at very high value. I personally cannot refer back to a time when duping didn’t exist and UT’s weren’t SB (a.k.a, the Wildshadow era; I started right at the end of it), but I’d be willing to guess that the economy was actually pretty stable and UT’s were fine the way they were (although there are more players = an influx of items, so this point is kind of mute).
As it stands right now, we don’t really know what would happen if UT’s were no longer SB. We can theorize, we can use examples, but there isn’t really much evidence or any hard cold numbers. And, like I said in my OG post, we cannot fairly compare UT’s to items in the past, nor try to really see what they’d do in the economy assuming duping was fixed. We know what happens to the value of items when duping does exist; we live in those times. But in a perfect world where all the nasty dupers are gone… then who knows. I just personally think that it wouldn’t be such a bad thing.