I think there's a lot of confusion in this area. A long term plan tends to become too rigid, making us unable to respond to change. If we are dealing with a complex problem
where the outcome is hard to predict this is a death sentence to the project.
On the other hand having only short term "agile" plans can on the extreme end turn us reactive and without any focus. If we are dealing with a "big" problem this is a death sentence for the project.
If the project is big complex and hard to predict we have to be able to be agile on both the short term and the long term, and sometimes on the really really long term, all at the same time. Oh, and also for the group and the whole organisation at the same time.
On the other hand having only short term "agile" plans can on the extreme end turn us reactive and without any focus. If we are dealing with a "big" problem this is a death sentence for the project.
If the project is big complex and hard to predict we have to be able to be agile on both the short term and the long term, and sometimes on the really really long term, all at the same time. Oh, and also for the group and the whole organisation at the same time.