Performance differences between fdw and view+fdw

Hello all,

I'm trying to understand a behavior I'm currently seeing while testing
mongo's fdw (using the mongo-c-driver 1.0 version).

Say I have a foreign table with 50 columns and 14000 rows, I also have a
view that does basically the same thing as querying the foreign table
directly except for a few castings.

Working with the foreign table directly, a query like select * from
foreign_table takes like 7 seconds, doing the same query but against the
view takes like 8.5 seconds

Another example, a select * from foreign_table where col = 'something'
takes like 12 ms but doing the same against the view takes like 110ms.

The only thing I could put the blame on when using the view is that inside
is the same query as working with the foreign table but I use casts for a
few columns like select col::text from foreign_table...

I don't know if anyone has tried mongo_fdw or something similar but I would
like to know if this behavior is normal and more importantly why the view
seems inefficient compared to query the foreign table directly (and without
casts)

Thanks in advance!!