For one player maybe. Of course, one player doing quick ventures isn't causing this issue, but rather the entire server doing them. When you have thousands of player characters per sever, each with two to eight retainers, producing a new item every hour, it's not unlikely that someone will get a specific item from that "very very large" pool of available items.
For a lower demand item, it doesn't take too many listings to drag the price down to desynth fodder. The players that obtained the items through quick ventures got the item for free, so the items hold a much lower value. It's only been a couple weeks and many items have dropped to lower than 5% of the previous going rate. The quick venture player has absolutely no issue drastically undercutting, since they invested practically nothing to obtain the item. It's also hard for actual crafters to compete with these types of players.
At the very least, I'd rather not have to compete with them.