5 has no dungeons because it doesn't need them.
Traversing the Da'ats is already a challenge on itself with all the different parts. The parking lot maze in Shinagawa, the upper and lower level paths in Chiyoda, the semi openess of Taito. Each daat has a small sub area that could be considered a dungeon on it's own. The so called dungeons are just breaks of pace.
I don't get why so many people fail to get that.