Max is good for level building.
No-one said it isn't but it isn't - the point is that Max is not a dedicated level builder and most FPS type games do not use Max to create their levels - UnrealED, WorldCraft etc etc - these are specialised apps Max is not - its more of an all purpose 3d content creation tool.
Of course depending on the type of game then Max may be suitable but when talking about interior game levels for FPS games I doubt whether any games exist where Max was used as the level builder and not one of the afore mentioned dedicated level builders.