Glatt and Chalak have different stringencies and leniencies relative to the other.
Not all sirchot are equal. There are certain areas of the lung, where
a sircha will not make the animal treif. However, there are differing
opinions as to the extent of these areas. The Sephardi view (following
the Beit Yosef) is more lenient – that is, according to them, there
are more areas where a sircha can exist without affecting the kashrut.
As a result, sirchot on certain areas of the lung can be ignored by
the Sephardim, while those same sirchot will make the entire animal
treif for Ashkenazim (following the Rama).
On the other hand, Ashkenazim are more lenient in handling those
sirchot found on the critical areas of the lung (where they can make
the animal treif). The Rama allows for these sirchot to be removed by
gentle peeling or squeezing, and if the lungs are then checked and
found to have no perforations, the meat is considered kosher. The Beit
Yosef strongly disagrees with this procedure stating that it is not
permissible to remove sirchot in any manner and thus they always
render the animal treif.
Some Ashkenazim follow another leniency whereby certain small, thin
sirchot which can be easily removed, are considered ‘ririn’ (mucous)
and do not affect the standard of kashrut (Beit David), regardless of
where it is located. Sephardim do not make this distinction.
Thus, an Ashkenzi cannot rely on the בית יוסף alone, and a ספרדי cannot rely on just Glatt Kosher, and neither is universally more machmir than the other.