I agree. Most of the Greeks were concentrated in the Alexandria area, which was declining. This may be one of the reasons why this area was neglected after the Arab conquest in favor of the foundation of Cairo.
Keep in mind that Alexandria was specifically founded (in much the same way Cairo and later Tunis in N Africa were) as a new, ethnically homogeneous capitol to rule over Egypt.
Alexandria had been Greek from the very beginning, predating Constantinople as a center of Hellenism for 600 years.
Hellenism (and later, Christianity) was so heavily ingrained in Egypt that even to this day there are 15-18 million Copts, and 8 million Christians.
This makes them by far the largest Christian population in the Middle East. Copts as an ethnic group have a larger population than any other 'Christian' population in the Eastern Med, including the Greeks.
It's not hard to understand why the Imperial government in Constantinople was unable to impose Orthodoxy on them.