Must admit I dont see the problem. - "Gain x happiness" is nice and simple. - Discovering tricks to solve the quest easier is part of the game play and if you dont want to experient you can go to the forum and get help or advice.
Quests arent a tutorial and shouldnt have step by step guides to the easiest way to solve them. Its quests and they contain problems that should be solved. Whether you do exactly what the quest says or if you want to experiment with finding an easier way to get the quest solved is up to you.
To my mind at least, thats not a bug but a feature. Gain x happiness is not misleading and I dont see why deleting housing should work. You dont gain happiness by that, you simply reduce the demand for it thus increasing the excess happiness in the town, but the happiness provided stays the same. - You could argue, or course, that deleting and rebuilding happiness buildings shouldnt work, but firstly you can actually argue that even though you delete happiness, you do actually gain happiness, secondly there could be some trouble in programming that although that could proably be solved by registering what level of total happiness the city has when the quest starts, thirdly it could make such quests nigh impossible or at least much too difficult. Not often, but for some situations i.e. a player has built a full city with ample happiness already. Especially with heavy diamond users that might have bought out the available squares for a city and setup their ideal city while being slow with the quests, this could be a problem.
Thats just my take of course, but I dont see the problem with the current wording.