Dupla Book and Peat Filtration

I was looking through my Dupla book The Optimum Aquarium.  On page 94 it says

"Peat filtration provides unfavorable conditions for water plants in the
aquarium.  Humic and yeast acids in peat have a negative effect on growth,
particularly in the first critical phase of the aquarium.  e.g. during the
first two months.  Such obstacles should be prevented.  In this connection we
should like to point out that bog wood placed in the aquarium may have the
same effect as peat.  In this case, we recommend a change of water, in order
to remove the bog wood leachings from the water.  Since in general water is
to be prepared with peat, a change of water is not practical."

Then I was looking in the archives and read that Duplagan is suspected of
being made up of mostly peat extract.  What gives?  Does peat hurt or help?