Fantasyland in Disneyworld is Little Mermaid, Snow White, Tangled, Beauty and the Beast yet no one says that is a jumbled mess.
Its more so the thematic architecture of the areas that work well and provide adequate flow within an area. Looking at all of those IPs listed for fantasy, they focus on wooded, Euro centric architecture and landscaping which make them visually fit together and transition to other areas through that same means.
IP lands are great but at the same time, you only have so many attractions that can be packed into one area due to the fact rides have to be canon to the IP which creates issues. Megaland with multiple IPs allow for way more IPs, attractions, and diversification to increase guest satisfaction etc. As many investors say, don't put all your eggs in one basket.