This is going to depend very heavily on where the dam is placed. Balbina is particularly bad because it sunk a ton of organic material with a bunch of acreage taken up.
I don't know that the dams in Canada are any better in terms of sunk organic material Williston reservoir in BC and the Manicouagan Reservoir are nearly as big and they didn't clear either of them. The Smallwood Reservoir is 3 times the size of Balbina's.
Yes he is using as an example what is probably the most inefficient dam in the world.