'Once Upon A Slime' is not a real quest and any other quester will tell you the same. It can hardly be called a bottle quest. I don't know why resources were even spent on something so asinine.
And yes, I know that today on the livestream it was noted that a quest was in development, albeit with no actual details on the subject. Please for the love of Zaros prioritize it.
For me personally it's not so much that there's a lack of quests but rather a lack of story advancement. Archaeology is a cool new method of adding story in the game without quests, though this was more so lore and world building rather than advancing the current story. Continuing this trend of merging story and traditional gameplay would be fine with me. In fact it might've been the needed solution for years. Quest engagement has historically been low because the format of quests are incongruent to the grindy gameplay of RS. I consider them the payoff of all that work, but I know that's not how at least half the playerbase feels. With that being the case I understand that they're given low priority and that's understandable, so why not apply the precepts of bottle quests for most quests? There's so much content and places in game that can be re-used even for the main storyline quests. Desperate Times was mostly like this. It seemed to have very few unique assets developed for it compared to other mainline story quests.
Whatever the case is going forward, the point stands that it's been a year since a real quest. Please don't put the quest that's in development on the backburner for any reason. The heart of RS deserves a proper quest soon.