They cover good points, however there really is no reason that anyone making a game should ever use the landscapes except for initial prototyping - and even then, those who choose to must be extremely aware that before shipping they likely have to replace everything with meshes in order to hit the performance requirements anyone would expect.
So, when should landscapes be used?
When prototyping, maybe.
And you should make sure not to use functions that lock you into them like the landscape grass for instance.
Or when not making a videogame.
But can’t the landscape system be optimized?
NO.
The only way to fix the increased costs it brings to your scene is to replace it with meshes.
So, even when prototyping, it’s likely better to just use something like Houdini.