The current system has it so that you must collect 3 items of the decoration item per level in order to move onto the next level. The problem with this system is that collecting decorations is limited daily (i.e. 10 Condensed Crystal Energy a day or various daily quests/content) and also random, which makes it extremely unreliable. If a player is unlucky, they might end up being entirely unable to progress in leveling up the globe because they are gated by the items at a specific level. (Not to mention the issue caused by the level gate with regards to crystals continuing to drop and being unable to be picked up.)
Realistically, it makes more sense to have "leveling up the globe" and "collecting decorations for the globe" be separate. That way a casual player can level up the globe and enjoy the few easy-to-obtain decorations they've collected, while a more dedicated player can hunt down the decorations they want for a more rewarding game experience. This model was followed by previous chair-customization events like Pink Bean's Mobile Mansion, Hashtag Chair, and Camila's Bakery events and worked fine. While I appreciate that this event has attempted to do something new by introducing a new element into an old formula, I think it negatively impacts enjoyment of the event in the end.