Custom scenario may be an option, but that depends of game creator, not of map creator. Also, you cannot depend on randomness when map is created (wastelands are fixed, even those that should be random) - so you can't have random warlord distribution.
Some interesting ideas. If I understand you correctly, the reason that you want an alternative approach to wastelands is that you want to be able to create a dead zone between regions on a map, which is possible but costly to break through?
That is only part of the idea. Like random wasteland, predefined wasteland areas (if used) will also make more or less toxic some bonuses. Let's say on the map https://www.warzone.com/SinglePlayer?PreviewMap=24843
i.e. Fall of Jerusalem - The Crusades, we want to put random wastelands, but also to protect citadels and fortresses from being taken initially as picks. Random wastelands may or not exclude player picks, but intentional wastelands would surely exclude them from picks. They may even have normal value, or increased value to make things tougher, or to put them to zero value.
On Small Earth map, we could have Peru, Western United State, East Africa, S. Europe mountainous (so excluded from picks, but also, with some start value), Western Australia, North Africa and Middle East as deserts (the same, possibly different value), Brasil, Congo, Indonesia and New Guinea as jungles, as example.
I didn't mean to shrink options in Small Earth map, but, as wasteland make things different on ladder games, predefined set of wastelands (by game creator) could also bring more diversity in future games.
Similar approach (as outcome, not as in map design) comes with maps like Biomes of America or Elitist Africa where some areas are more desirable than others due to increased values or penalties.