Oh, come on, let's at least be honest.
First off, Global Trade HQ has not been' a very popular feature'. Basically every other post on here is people complaining about it, and for good reason; it's incredibly frustrating.
I do agree that a search feature would probably be less helpful than we might all like to think, given that it would do nothing to prevent items from selling before you could click through to them. However, you're cheerfully ignoring the massive frustration involved in repeatedly opening, scrolling through, closing and re-opening the Trade HQ just for the possibility of getting to the point of clicking on an item. Which will be gone before you get to it, because the high-demand items already 'sell incredibly fast'. It is, literally, possible to spend hours attempting to buy an item and still not be successful. This is not a functional system, and none of the tweaking you've done so far has made it so.
I find the mention of 'supply and demand' entirely disingenuous. In a genuine marketplace, supply and demand is key; in the Global Trade HQ it's of very limited practical relevance because we have no way of knowing a) how much supply there is of any given item or b) how much demand there is. At best, individual players can observe something along the lines of "look, lots of doughnuts; perhaps that means fewer people want doughnuts than are selling them"; but it's terribly hit and miss. Without access to something along the lines of a search function it's not possible to get any real sense of the relative availability of items and make decisions about what to sell/buy. It's all just guesswork and luck.
Equally, regarding travel to other cities - I actually do enjoy looking at other cities, but it's generally the last thing I want to do when I'm actively trying to buy something, because I know that process will take foooooooooorrrrrrrrrrrrreeeeeeeeevvvvvvveeeeeeerrrrrrrrrrrrrrrrrr and don't want to interrupt it by sightseeing. The option to visit and view cities is great (and I'd actually like to be able to go one further, and be able to 'friend' cities I've visited and found interesting) but there is absolutely no logical reason why this function needs to be combined with the Trade HQ; and, in fact, doing so creates a delay in purchasing items that must surely disadvantage anyone playing on a slower device or with a slower connection. That unequal, unfair experience you're so concerned about? You've created it yourselves, apparently on purpose, and persist in defending it rather than addressing the issue.
Personally, I'd be in favour of a genuinely supply-and-demand based system, where players can place an order and sellers can fill it, and a genuine sense of supply and demand can enter into transactions; coupled with a sightseeing option allowing you to visit other cities just to take a look.